diff --git a/NEWS b/NEWS
index 1b3751bd..24d4525c 100644
--- a/NEWS
+++ b/NEWS
@@ -1,11 +1,13 @@
 ==========================
 
+ * New API for creating FileRef from IOStream.
  * Added support for ID3v2 PCST and WFED frames.
  * Added String::clear().
  * Better handling of duplicate ID3v2 tags in all kinds of files.
  * Better handling of duplicate tags in WAV files.
  * Fixed crash when calling File::properties() after strip().
  * Fixed possible file corruptions when saving ASF files.
+ * Fixed updating the comment field of Vorbis comments.
  * Marked ByteVector::null and ByteVector::isNull() deprecated.
  * Marked String::null and ByteVector::isNull() deprecated.
  * Many smaller bug fixes and performance improvements.
diff --git a/taglib/CMakeLists.txt b/taglib/CMakeLists.txt
index 29624f2e..ed84805b 100644
--- a/taglib/CMakeLists.txt
+++ b/taglib/CMakeLists.txt
@@ -362,6 +362,7 @@ set(tag_LIB_SRCS
   tagunion.cpp
   fileref.cpp
   audioproperties.cpp
+  tagutils.cpp
 )
 
 add_library(tag ${tag_LIB_SRCS} ${tag_HDRS})
diff --git a/taglib/ape/apefile.cpp b/taglib/ape/apefile.cpp
index 232e0c2b..59510c12 100644
--- a/taglib/ape/apefile.cpp
+++ b/taglib/ape/apefile.cpp
@@ -38,9 +38,9 @@
 #include <id3v1tag.h>
 #include <id3v2header.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include "apefile.h"
-
 #include "apetag.h"
 #include "apefooter.h"
 
@@ -248,7 +248,7 @@ void APE::File::read(bool readProperties)
 {
   // Look for an ID3v2 tag
 
-  d->ID3v2Location = findID3v2();
+  d->ID3v2Location = Utils::findID3v2(this);
 
   if(d->ID3v2Location >= 0) {
     seek(d->ID3v2Location);
@@ -259,7 +259,7 @@ void APE::File::read(bool readProperties)
 
   // Look for an ID3v1 tag
 
-  d->ID3v1Location = findID3v1();
+  d->ID3v1Location = Utils::findID3v1(this);
 
   if(d->ID3v1Location >= 0) {
     d->tag.set(ApeID3v1Index, new ID3v1::Tag(this, d->ID3v1Location));
@@ -268,7 +268,7 @@ void APE::File::read(bool readProperties)
 
   // Look for an APE tag
 
-  d->APELocation = findAPE();
+  d->APELocation = Utils::findAPE(this, d->ID3v1Location);
 
   if(d->APELocation >= 0) {
     d->tag.set(ApeAPEIndex, new APE::Tag(this, d->APELocation));
@@ -304,48 +304,3 @@ void APE::File::read(bool readProperties)
     d->properties = new AudioProperties(this, streamLength);
   }
 }
-
-offset_t APE::File::findAPE()
-{
-  if(!isValid())
-    return -1;
-
-  if(d->hasID3v1)
-    seek(-160, End);
-  else
-    seek(-32, End);
-
-  offset_t p = tell();
-
-  if(readBlock(8) == APE::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
-
-offset_t APE::File::findID3v1()
-{
-  if(!isValid())
-    return -1;
-
-  seek(-128, End);
-  offset_t p = tell();
-
-  if(readBlock(3) == ID3v1::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
-
-offset_t APE::File::findID3v2()
-{
-  if(!isValid())
-    return -1;
-
-  seek(0);
-
-  if(readBlock(3) == ID3v2::Header::fileIdentifier())
-    return 0;
-
-  return -1;
-}
diff --git a/taglib/ape/apefile.h b/taglib/ape/apefile.h
index 5620fc4f..c9c728ea 100644
--- a/taglib/ape/apefile.h
+++ b/taglib/ape/apefile.h
@@ -206,9 +206,6 @@ namespace TagLib {
       File &operator=(const File &);
 
       void read(bool readProperties);
-      offset_t findAPE();
-      offset_t findID3v1();
-      offset_t findID3v2();
 
       class FilePrivate;
       FilePrivate *d;
diff --git a/taglib/ape/apeitem.cpp b/taglib/ape/apeitem.cpp
index 534fb102..51b1fccd 100644
--- a/taglib/ape/apeitem.cpp
+++ b/taglib/ape/apeitem.cpp
@@ -197,7 +197,7 @@ String APE::Item::toString() const
   if(d->type == Text && !isEmpty())
     return d->text.front();
   else
-    return String::null;
+    return String();
 }
 
 bool APE::Item::isEmpty() const
diff --git a/taglib/ape/apetag.cpp b/taglib/ape/apetag.cpp
index baaad7c2..1d0f62b3 100644
--- a/taglib/ape/apetag.cpp
+++ b/taglib/ape/apetag.cpp
@@ -81,35 +81,35 @@ ByteVector APE::Tag::fileIdentifier()
 String APE::Tag::title() const
 {
   if(d->itemListMap["TITLE"].isEmpty())
-    return String::null;
+    return String();
   return d->itemListMap["TITLE"].values().toString();
 }
 
 String APE::Tag::artist() const
 {
   if(d->itemListMap["ARTIST"].isEmpty())
-    return String::null;
+    return String();
   return d->itemListMap["ARTIST"].values().toString();
 }
 
 String APE::Tag::album() const
 {
   if(d->itemListMap["ALBUM"].isEmpty())
-    return String::null;
+    return String();
   return d->itemListMap["ALBUM"].values().toString();
 }
 
 String APE::Tag::comment() const
 {
   if(d->itemListMap["COMMENT"].isEmpty())
-    return String::null;
+    return String();
   return d->itemListMap["COMMENT"].values().toString();
 }
 
 String APE::Tag::genre() const
 {
   if(d->itemListMap["GENRE"].isEmpty())
-    return String::null;
+    return String();
   return d->itemListMap["GENRE"].values().toString();
 }
 
@@ -188,7 +188,7 @@ PropertyMap APE::Tag::properties() const
     String tagName = it->first.upper();
     // if the item is Binary or Locator, or if the key is an invalid string,
     // add to unsupportedData
-    if(it->second.type() != Item::Text || tagName.isNull())
+    if(it->second.type() != Item::Text || tagName.isEmpty())
       properties.unsupportedData().append(it->first);
     else {
       // Some tags need to be handled specially
@@ -225,7 +225,7 @@ PropertyMap APE::Tag::setProperties(const PropertyMap &origProps)
   for(; remIt != itemListMap().end(); ++remIt) {
     String key = remIt->first.upper();
     // only remove if a) key is valid, b) type is text, c) key not contained in new properties
-    if(!key.isNull() && remIt->second.type() == APE::Item::Text && !properties.contains(key))
+    if(!key.isEmpty() && remIt->second.type() == APE::Item::Text && !properties.contains(key))
       toRemove.append(remIt->first);
   }
 
diff --git a/taglib/asf/asftag.cpp b/taglib/asf/asftag.cpp
index 5b61a024..ea9141a3 100644
--- a/taglib/asf/asftag.cpp
+++ b/taglib/asf/asftag.cpp
@@ -64,7 +64,7 @@ String ASF::Tag::album() const
 {
   if(d->attributeListMap.contains("WM/AlbumTitle"))
     return d->attributeListMap["WM/AlbumTitle"][0].toString();
-  return String::null;
+  return String();
 }
 
 String ASF::Tag::copyright() const
@@ -107,7 +107,7 @@ String ASF::Tag::genre() const
 {
   if(d->attributeListMap.contains("WM/Genre"))
     return d->attributeListMap["WM/Genre"][0].toString();
-  return String::null;
+  return String();
 }
 
 void ASF::Tag::setTitle(const String &value)
@@ -329,16 +329,16 @@ PropertyMap ASF::Tag::setProperties(const PropertyMap &props)
   for(; it != origProps.end(); ++it) {
     if(!props.contains(it->first) || props[it->first].isEmpty()) {
       if(it->first == "TITLE") {
-        d->title = String::null;
+        d->title.clear();
       }
       else if(it->first == "ARTIST") {
-        d->artist = String::null;
+        d->artist.clear();
       }
       else if(it->first == "COMMENT") {
-        d->comment = String::null;
+        d->comment.clear();
       }
       else if(it->first == "COPYRIGHT") {
-        d->copyright = String::null;
+        d->copyright.clear();
       }
       else {
         d->attributeListMap.erase(reverseKeyMap[it->first]);
diff --git a/taglib/fileref.cpp b/taglib/fileref.cpp
index 5d8c25de..eb3f5275 100644
--- a/taglib/fileref.cpp
+++ b/taglib/fileref.cpp
@@ -27,10 +27,10 @@
  *   http://www.mozilla.org/MPL/                                           *
  ***************************************************************************/
 
-#include "tfile.h"
-#include "tstring.h"
-#include "tdebug.h"
-#include "tsmartptr.h"
+#include <tfile.h>
+#include <tstring.h>
+#include <tdebug.h>
+#include <tsmartptr.h>
 
 #include "fileref.h"
 #include "asffile.h"
@@ -58,91 +58,129 @@ using namespace TagLib;
 namespace
 {
   typedef List<const FileRef::FileTypeResolver *> ResolverList;
-  typedef ResolverList::ConstIterator ResolverConstIterator;
-
   ResolverList fileTypeResolvers;
 
-  SHARED_PTR<File> create(
-    FileName fileName,
-    bool readAudioProperties,
-    AudioProperties::ReadStyle audioPropertiesStyle)
+  // Templatized internal functions. T should be String or IOStream*.
+
+  template <typename T>
+  inline FileName toFileName(T arg)
   {
-    SHARED_PTR<File> file;
-    for(ResolverConstIterator it = fileTypeResolvers.begin(); it != fileTypeResolvers.end(); ++it)
-    {
-      file.reset((*it)->createFile(fileName, readAudioProperties, audioPropertiesStyle));
+    // Should never be called.
+  }
+
+  template <>
+  inline FileName toFileName<IOStream *>(IOStream *arg)
+  {
+    return arg->name();
+  }
+
+  template <>
+  inline FileName toFileName<FileName>(FileName arg)
+  {
+    return arg;
+  }
+
+  template <typename T>
+  inline File *resolveFileType(T arg, bool readProperties,
+                               AudioProperties::ReadStyle style)
+  {
+    // Should never be called.
+  }
+
+  template <>
+  inline File *resolveFileType<IOStream *>(IOStream *arg, bool readProperties,
+                                           AudioProperties::ReadStyle style)
+  {
+    return 0;
+  }
+
+  template <>
+  inline File *resolveFileType<FileName>(FileName arg, bool readProperties,
+                                         AudioProperties::ReadStyle style)
+  {
+    ResolverList::ConstIterator it = fileTypeResolvers.begin();
+    for(; it != fileTypeResolvers.end(); ++it) {
+      File *file = (*it)->createFile(arg, readProperties, style);
       if(file)
         return file;
     }
 
-    String ext;
-    {
+    return 0;
+  }
+
+  template <typename T>
+  File* createInternal(T arg, bool readAudioProperties,
+                       AudioProperties::ReadStyle audioPropertiesStyle)
+  {
+    File *file = resolveFileType(arg, readAudioProperties, audioPropertiesStyle);
+    if(file)
+      return file;
+
 #ifdef _WIN32
-
-      String s = fileName.toString();
-
+    const String s = toFileName(arg).toString();
 #else
-
-      String s = fileName;
-
+    const String s(toFileName(arg));
 #endif
 
-      const size_t pos = s.rfind(".");
-      if(pos != String::npos())
-        ext = s.substr(pos + 1).upper();
-    }
+    String ext;
+    const int pos = s.rfind(".");
+    if(pos != -1)
+      ext = s.substr(pos + 1).upper();
 
     // If this list is updated, the method defaultFileExtensions() should also be
     // updated.  However at some point that list should be created at the same time
     // that a default file type resolver is created.
 
-    if(!ext.isEmpty()) {
-      if(ext == "MP3")
-        file.reset(new MPEG::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "OGG")
-        file.reset(new Ogg::Vorbis::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "OGA") {
-        /* .oga can be any audio in the Ogg container. First try FLAC, then Vorbis. */
-        file.reset(new Ogg::FLAC::File(fileName, readAudioProperties, audioPropertiesStyle));
-        if(!file->isValid())
-          file.reset(new Ogg::Vorbis::File(fileName, readAudioProperties, audioPropertiesStyle));
-      }
-      else if(ext == "FLAC")
-        file.reset(new FLAC::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "MPC")
-        file.reset(new MPC::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "WV")
-        file.reset(new WavPack::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "SPX")
-        file.reset(new Ogg::Speex::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "OPUS")
-        file.reset(new Ogg::Opus::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "TTA")
-        file.reset(new TrueAudio::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "M4A" || ext == "M4R" || ext == "M4B" || ext == "M4P" || ext == "MP4" || ext == "3G2")
-        file.reset(new MP4::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "WMA" || ext == "ASF")
-        file.reset(new ASF::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "AIF" || ext == "AIFF" || ext == "AFC" || ext == "AIFC")
-        file.reset(new RIFF::AIFF::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "WAV")
-        file.reset(new RIFF::WAV::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "APE")
-        file.reset(new APE::File(fileName, readAudioProperties, audioPropertiesStyle));
-      // module, nst and wow are possible but uncommon extensions
-      else if(ext == "MOD" || ext == "MODULE" || ext == "NST" || ext == "WOW")
-        file.reset(new Mod::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "S3M")
-        file.reset(new S3M::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "IT")
-        file.reset(new IT::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "XM")
-        file.reset(new XM::File(fileName, readAudioProperties, audioPropertiesStyle));
-      else if(ext == "DSF")
-        file.reset(new DSF::File(fileName, readAudioProperties, audioPropertiesStyle));
-    }
+    if(ext.isEmpty())
+      return 0;
 
-    return file;
+    if(ext == "MP3")
+      return new MPEG::File(arg, ID3v2::FrameFactory::instance(), readAudioProperties, audioPropertiesStyle);
+    if(ext == "OGG")
+      return new Ogg::Vorbis::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "OGA") {
+      /* .oga can be any audio in the Ogg container. First try FLAC, then Vorbis. */
+      File *file = new Ogg::FLAC::File(arg, readAudioProperties, audioPropertiesStyle);
+      if(file->isValid())
+        return file;
+      delete file;
+      return new Ogg::Vorbis::File(arg, readAudioProperties, audioPropertiesStyle);
+    }
+    if(ext == "FLAC")
+      return new FLAC::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "MPC")
+      return new MPC::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "WV")
+      return new WavPack::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "SPX")
+      return new Ogg::Speex::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "OPUS")
+      return new Ogg::Opus::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "TTA")
+      return new TrueAudio::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "M4A" || ext == "M4R" || ext == "M4B" || ext == "M4P" || ext == "MP4" || ext == "3G2")
+      return new MP4::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "WMA" || ext == "ASF")
+      return new ASF::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "AIF" || ext == "AIFF" || ext == "AFC" || ext == "AIFC")
+      return new RIFF::AIFF::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "WAV")
+      return new RIFF::WAV::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "APE")
+      return new APE::File(arg, readAudioProperties, audioPropertiesStyle);
+    // module, nst and wow are possible but uncommon extensions
+    if(ext == "MOD" || ext == "MODULE" || ext == "NST" || ext == "WOW")
+      return new Mod::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "S3M")
+      return new S3M::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "IT")
+      return new IT::File(arg, readAudioProperties, audioPropertiesStyle);
+    if(ext == "XM")
+      return new XM::File(arg, readAudioProperties, audioPropertiesStyle);
+    if (ext == "DSF")
+      return new DSF::File(arg, readAudioProperties, audioPropertiesStyle);
+
+    return 0;
   }
 }
 
@@ -170,8 +208,14 @@ FileRef::FileRef() :
 {
 }
 
-FileRef::FileRef(FileName fileName, bool readAudioProperties, AudioProperties::ReadStyle style) :
-  d(new FileRefPrivate(create(fileName, readAudioProperties, style)))
+FileRef::FileRef(FileName fileName, bool readAudioProperties,
+                 AudioProperties::ReadStyle audioPropertiesStyle) :
+  d(new FileRefPrivate(createInternal(fileName, readAudioProperties, audioPropertiesStyle)))
+{
+}
+
+FileRef::FileRef(IOStream* stream, bool readAudioProperties, AudioProperties::ReadStyle audioPropertiesStyle) :
+  d(new FileRefPrivate(createInternal(stream, readAudioProperties, audioPropertiesStyle)))
 {
 }
 
@@ -306,16 +350,23 @@ bool FileRef::isNull() const
 
 FileRef &FileRef::operator=(const FileRef &ref)
 {
-  *d = *ref.d;
+  FileRef(ref).swap(*this);
   return *this;
 }
 
+void FileRef::swap(FileRef &ref)
+{
+  using std::swap;
+
+  swap(d, ref.d);
+}
+
 bool FileRef::operator==(const FileRef &ref) const
 {
-  return (d->file == ref.d->file);
+  return (ref.d->file == d->file);
 }
 
 bool FileRef::operator!=(const FileRef &ref) const
 {
-  return (d->file != ref.d->file);
+  return (ref.d->file != d->file);
 }
diff --git a/taglib/fileref.h b/taglib/fileref.h
index 0b149924..71126aba 100644
--- a/taglib/fileref.h
+++ b/taglib/fileref.h
@@ -128,6 +128,20 @@ namespace TagLib {
                      AudioProperties::ReadStyle
                      audioPropertiesStyle = AudioProperties::Average);
 
+    /*!
+     * Construct a FileRef from an opened \a IOStream.  If \a readAudioProperties is true then
+     * the audio properties will be read using \a audioPropertiesStyle.  If
+     * \a readAudioProperties is false then \a audioPropertiesStyle will be
+     * ignored.
+     *
+     * Also see the note in the class documentation about why you may not want to
+     * use this method in your application.
+     */
+    explicit FileRef(IOStream* stream,
+                     bool readAudioProperties = true,
+                     AudioProperties::ReadStyle
+                     audioPropertiesStyle = AudioProperties::Average);
+
     /*!
      * Construct a FileRef using \a file.  The FileRef now takes ownership of the
      * pointer and will delete the File when it passes out of scope.
@@ -271,6 +285,11 @@ namespace TagLib {
      */
     FileRef &operator=(const FileRef &ref);
 
+    /*!
+     * Exchanges the content of the FileRef by the content of \a ref.
+     */
+    void swap(FileRef &ref);
+
     /*!
      * Returns true if this FileRef and \a ref point to the same File object.
      */
diff --git a/taglib/flac/flacfile.cpp b/taglib/flac/flacfile.cpp
index faf1cc80..045dfdec 100644
--- a/taglib/flac/flacfile.cpp
+++ b/taglib/flac/flacfile.cpp
@@ -29,6 +29,7 @@
 #include <tdebug.h>
 #include <tagunion.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include <id3v2header.h>
 #include <id3v2tag.h>
@@ -330,7 +331,7 @@ void FLAC::File::read(bool readProperties)
 {
   // Look for an ID3v2 tag
 
-  d->ID3v2Location = findID3v2();
+  d->ID3v2Location = Utils::findID3v2(this);
 
   if(d->ID3v2Location >= 0) {
 
@@ -346,7 +347,7 @@ void FLAC::File::read(bool readProperties)
 
   // Look for an ID3v1 tag
 
-  d->ID3v1Location = findID3v1();
+  d->ID3v1Location = Utils::findID3v1(this);
 
   if(d->ID3v1Location >= 0) {
     d->tag.set(FlacID3v1Index, new ID3v1::Tag(this, d->ID3v1Location));
@@ -507,30 +508,3 @@ void FLAC::File::scan()
 
   d->scanned = true;
 }
-
-offset_t FLAC::File::findID3v1()
-{
-  if(!isValid())
-    return -1;
-
-  seek(-128, End);
-  offset_t p = tell();
-
-  if(readBlock(3) == ID3v1::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
-
-offset_t FLAC::File::findID3v2()
-{
-  if(!isValid())
-    return -1;
-
-  seek(0);
-
-  if(readBlock(3) == ID3v2::Header::fileIdentifier())
-    return 0;
-
-  return -1;
-}
diff --git a/taglib/flac/flacfile.h b/taglib/flac/flacfile.h
index 002a3c5e..f17df67e 100644
--- a/taglib/flac/flacfile.h
+++ b/taglib/flac/flacfile.h
@@ -257,8 +257,6 @@ namespace TagLib {
 
       void read(bool readProperties);
       void scan();
-      offset_t findID3v2();
-      offset_t findID3v1();
 
       class FilePrivate;
       FilePrivate *d;
diff --git a/taglib/it/itfile.cpp b/taglib/it/itfile.cpp
index e7f89dc2..6b7168fd 100644
--- a/taglib/it/itfile.cpp
+++ b/taglib/it/itfile.cpp
@@ -108,7 +108,7 @@ bool IT::File::save()
     if(i < lines.size())
       writeString(lines[i], 25);
     else
-      writeString(String::null, 25);
+      writeString(String(), 25);
     writeByte(0);
   }
 
@@ -123,7 +123,7 @@ bool IT::File::save()
     if((TagLib::uint)(i + instrumentCount) < lines.size())
       writeString(lines[i + instrumentCount], 25);
     else
-      writeString(String::null, 25);
+      writeString(String(), 25);
     writeByte(0);
   }
 
diff --git a/taglib/mod/modfile.cpp b/taglib/mod/modfile.cpp
index b3fc176b..5872cad5 100644
--- a/taglib/mod/modfile.cpp
+++ b/taglib/mod/modfile.cpp
@@ -89,7 +89,7 @@ bool Mod::File::save()
   }
 
   for(uint i = n; i < d->properties.instrumentCount(); ++ i) {
-    writeString(String::null, 22);
+    writeString(String(), 22);
     seek(8, Current);
   }
   return true;
diff --git a/taglib/mod/modtag.cpp b/taglib/mod/modtag.cpp
index 4ba72117..af98fb92 100644
--- a/taglib/mod/modtag.cpp
+++ b/taglib/mod/modtag.cpp
@@ -55,12 +55,12 @@ String Mod::Tag::title() const
 
 String Mod::Tag::artist() const
 {
-  return String::null;
+  return String();
 }
 
 String Mod::Tag::album() const
 {
-  return String::null;
+  return String();
 }
 
 String Mod::Tag::comment() const
@@ -70,7 +70,7 @@ String Mod::Tag::comment() const
 
 String Mod::Tag::genre() const
 {
-  return String::null;
+  return String();
 }
 
 TagLib::uint Mod::Tag::year() const
@@ -128,7 +128,7 @@ PropertyMap Mod::Tag::properties() const
   PropertyMap properties;
   properties["TITLE"] = d->title;
   properties["COMMENT"] = d->comment;
-  if(!(d->trackerName.isNull()))
+  if(!(d->trackerName.isEmpty()))
     properties["TRACKERNAME"] = d->trackerName;
   return properties;
 }
@@ -142,19 +142,19 @@ PropertyMap Mod::Tag::setProperties(const PropertyMap &origProps)
     d->title = properties["TITLE"].front();
     oneValueSet.append("TITLE");
   } else
-    d->title = String::null;
+    d->title.clear();
 
   if(properties.contains("COMMENT")) {
     d->comment = properties["COMMENT"].front();
     oneValueSet.append("COMMENT");
   } else
-    d->comment = String::null;
+    d->comment.clear();
 
   if(properties.contains("TRACKERNAME")) {
     d->trackerName = properties["TRACKERNAME"].front();
     oneValueSet.append("TRACKERNAME");
   } else
-    d->trackerName = String::null;
+    d->trackerName.clear();
 
   // for each tag that has been set above, remove the first entry in the corresponding
   // value list. The others will be returned as unsupported by this format.
diff --git a/taglib/mp4/mp4tag.cpp b/taglib/mp4/mp4tag.cpp
index 7d1dff6f..50f1a0fb 100644
--- a/taglib/mp4/mp4tag.cpp
+++ b/taglib/mp4/mp4tag.cpp
@@ -686,7 +686,7 @@ MP4::Tag::title() const
 {
   if(d->items.contains("\251nam"))
     return d->items["\251nam"].toStringList().toString(", ");
-  return String::null;
+  return String();
 }
 
 String
@@ -694,7 +694,7 @@ MP4::Tag::artist() const
 {
   if(d->items.contains("\251ART"))
     return d->items["\251ART"].toStringList().toString(", ");
-  return String::null;
+  return String();
 }
 
 String
@@ -702,7 +702,7 @@ MP4::Tag::album() const
 {
   if(d->items.contains("\251alb"))
     return d->items["\251alb"].toStringList().toString(", ");
-  return String::null;
+  return String();
 }
 
 String
@@ -710,7 +710,7 @@ MP4::Tag::comment() const
 {
   if(d->items.contains("\251cmt"))
     return d->items["\251cmt"].toStringList().toString(", ");
-  return String::null;
+  return String();
 }
 
 String
@@ -718,7 +718,7 @@ MP4::Tag::genre() const
 {
   if(d->items.contains("\251gen"))
     return d->items["\251gen"].toStringList().toString(", ");
-  return String::null;
+  return String();
 }
 
 unsigned int
diff --git a/taglib/mpc/mpcfile.cpp b/taglib/mpc/mpcfile.cpp
index e24d7083..06cd2b2f 100644
--- a/taglib/mpc/mpcfile.cpp
+++ b/taglib/mpc/mpcfile.cpp
@@ -28,6 +28,7 @@
 #include <tagunion.h>
 #include <tdebug.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include "mpcfile.h"
 #include "id3v1tag.h"
@@ -256,7 +257,7 @@ void MPC::File::read(bool readProperties)
 {
   // Look for an ID3v1 tag
 
-  d->ID3v1Location = findID3v1();
+  d->ID3v1Location = Utils::findID3v1(this);
 
   if(d->ID3v1Location >= 0) {
     d->tag.set(MPCID3v1Index, new ID3v1::Tag(this, d->ID3v1Location));
@@ -265,7 +266,7 @@ void MPC::File::read(bool readProperties)
 
   // Look for an APE tag
 
-  d->APELocation = findAPE();
+  d->APELocation = Utils::findAPE(this, d->ID3v1Location);
 
   if(d->APELocation >= 0) {
     d->tag.set(MPCAPEIndex, new APE::Tag(this, d->APELocation));
@@ -280,7 +281,7 @@ void MPC::File::read(bool readProperties)
 
   // Look for an ID3v2 tag
 
-  d->ID3v2Location = findID3v2();
+  d->ID3v2Location = Utils::findID3v2(this);
 
   if(d->ID3v2Location >= 0) {
     seek(d->ID3v2Location);
@@ -313,48 +314,3 @@ void MPC::File::read(bool readProperties)
     d->properties = new AudioProperties(this, streamLength);
   }
 }
-
-offset_t MPC::File::findAPE()
-{
-  if(!isValid())
-    return -1;
-
-  if(d->hasID3v1)
-    seek(-160, End);
-  else
-    seek(-32, End);
-
-  offset_t p = tell();
-
-  if(readBlock(8) == APE::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
-
-offset_t MPC::File::findID3v1()
-{
-  if(!isValid())
-    return -1;
-
-  seek(-128, End);
-  offset_t p = tell();
-
-  if(readBlock(3) == ID3v1::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
-
-offset_t MPC::File::findID3v2()
-{
-  if(!isValid())
-    return -1;
-
-  seek(0);
-
-  if(readBlock(3) == ID3v2::Header::fileIdentifier())
-    return 0;
-
-  return -1;
-}
diff --git a/taglib/mpc/mpcfile.h b/taglib/mpc/mpcfile.h
index 9cdaef1e..5ffdf0f3 100644
--- a/taglib/mpc/mpcfile.h
+++ b/taglib/mpc/mpcfile.h
@@ -213,9 +213,6 @@ namespace TagLib {
       File &operator=(const File &);
 
       void read(bool readProperties);
-      offset_t findAPE();
-      offset_t findID3v1();
-      offset_t findID3v2();
 
       class FilePrivate;
       FilePrivate *d;
diff --git a/taglib/mpeg/id3v1/id3v1tag.cpp b/taglib/mpeg/id3v1/id3v1tag.cpp
index 39798745..06b49830 100644
--- a/taglib/mpeg/id3v1/id3v1tag.cpp
+++ b/taglib/mpeg/id3v1/id3v1tag.cpp
@@ -182,7 +182,7 @@ void ID3v1::Tag::setGenre(const String &s)
 
 void ID3v1::Tag::setYear(TagLib::uint i)
 {
-  d->year = i > 0 ? String::number(i) : String::null;
+  d->year = i > 0 ? String::number(i) : String();
 }
 
 void ID3v1::Tag::setTrack(TagLib::uint i)
diff --git a/taglib/mpeg/id3v2/frames/commentsframe.cpp b/taglib/mpeg/id3v2/frames/commentsframe.cpp
index deaa9d9a..b5618322 100644
--- a/taglib/mpeg/id3v2/frames/commentsframe.cpp
+++ b/taglib/mpeg/id3v2/frames/commentsframe.cpp
@@ -116,8 +116,6 @@ PropertyMap CommentsFrame::asProperties() const
   PropertyMap map;
   if(key.isEmpty() || key == "COMMENT")
     map.insert("COMMENT", text());
-  else if(key.isNull())
-    map.unsupportedData().append(L"COMM/" + description());
   else
     map.insert("COMMENT:" + key, text());
   return map;
@@ -164,7 +162,7 @@ void CommentsFrame::parseFields(const ByteVector &data)
     } else {
       d->description = String(l.front(), d->textEncoding);
       d->text = String(l.back(), d->textEncoding);
-    }  
+    }
   }
 }
 
diff --git a/taglib/mpeg/id3v2/frames/synchronizedlyricsframe.cpp b/taglib/mpeg/id3v2/frames/synchronizedlyricsframe.cpp
index 2a4c6663..f00a39af 100644
--- a/taglib/mpeg/id3v2/frames/synchronizedlyricsframe.cpp
+++ b/taglib/mpeg/id3v2/frames/synchronizedlyricsframe.cpp
@@ -159,7 +159,7 @@ void SynchronizedLyricsFrame::parseFields(const ByteVector &data)
   size_t pos = 6;
 
   d->description = readStringField(data, d->textEncoding, pos);
-  if(d->description.isNull())
+  if(d->description.isEmpty())
     return;
 
   /*
@@ -190,7 +190,7 @@ void SynchronizedLyricsFrame::parseFields(const ByteVector &data)
       }
     }
     String text = readStringField(data, enc, pos);
-    if(text.isNull() || pos + 4 > end)
+    if(text.isEmpty() || pos + 4 > end)
       return;
 
     uint time = data.toUInt32BE(pos);
diff --git a/taglib/mpeg/id3v2/frames/tableofcontentsframe.cpp b/taglib/mpeg/id3v2/frames/tableofcontentsframe.cpp
index a3598398..8d659cc5 100644
--- a/taglib/mpeg/id3v2/frames/tableofcontentsframe.cpp
+++ b/taglib/mpeg/id3v2/frames/tableofcontentsframe.cpp
@@ -214,7 +214,7 @@ void TableOfContentsFrame::removeEmbeddedFrames(const ByteVector &id)
 
 String TableOfContentsFrame::toString() const
 {
-  return String::null;
+  return String();
 }
 
 PropertyMap TableOfContentsFrame::asProperties() const
diff --git a/taglib/mpeg/id3v2/frames/textidentificationframe.cpp b/taglib/mpeg/id3v2/frames/textidentificationframe.cpp
index d32ecc5f..7fc40a5f 100644
--- a/taglib/mpeg/id3v2/frames/textidentificationframe.cpp
+++ b/taglib/mpeg/id3v2/frames/textidentificationframe.cpp
@@ -295,7 +295,7 @@ PropertyMap TextIdentificationFrame::makeTMCLProperties() const
   StringList l = fieldList();
   for(StringList::ConstIterator it = l.begin(); it != l.end(); ++it) {
     String instrument = it->upper();
-    if(instrument.isNull()) {
+    if(instrument.isEmpty()) {
       // instrument is not a valid key -> frame unsupported
       map.clear();
       map.unsupportedData().append(frameID());
@@ -315,8 +315,8 @@ UserTextIdentificationFrame::UserTextIdentificationFrame(String::Type encoding)
   d(0)
 {
   StringList l;
-  l.append(String::null);
-  l.append(String::null);
+  l.append(String());
+  l.append(String());
   setText(l);
 }
 
@@ -344,7 +344,7 @@ String UserTextIdentificationFrame::description() const
 {
   return !TextIdentificationFrame::fieldList().isEmpty()
     ? TextIdentificationFrame::fieldList().front()
-    : String::null;
+    : String();
 }
 
 StringList UserTextIdentificationFrame::fieldList() const
@@ -357,7 +357,7 @@ StringList UserTextIdentificationFrame::fieldList() const
 void UserTextIdentificationFrame::setText(const String &text)
 {
   if(description().isEmpty())
-    setDescription(String::null);
+    setDescription(String());
 
   TextIdentificationFrame::setText(StringList(description()).append(text));
 }
@@ -365,7 +365,7 @@ void UserTextIdentificationFrame::setText(const String &text)
 void UserTextIdentificationFrame::setText(const StringList &fields)
 {
   if(description().isEmpty())
-    setDescription(String::null);
+    setDescription(String());
 
   TextIdentificationFrame::setText(StringList(description()).append(fields));
 }
@@ -420,7 +420,7 @@ void UserTextIdentificationFrame::checkFields()
   const size_t fields = fieldList().size();
 
   if(fields == 0)
-    setDescription(String::null);
+    setDescription(String());
   if(fields <= 1)
-    setText(String::null);
+    setText(String());
 }
diff --git a/taglib/mpeg/id3v2/frames/uniquefileidentifierframe.cpp b/taglib/mpeg/id3v2/frames/uniquefileidentifierframe.cpp
index 1d30b799..eef4e51e 100644
--- a/taglib/mpeg/id3v2/frames/uniquefileidentifierframe.cpp
+++ b/taglib/mpeg/id3v2/frames/uniquefileidentifierframe.cpp
@@ -86,7 +86,7 @@ void UniqueFileIdentifierFrame::setIdentifier(const ByteVector &v)
 
 String UniqueFileIdentifierFrame::toString() const
 {
-  return String::null;
+  return String();
 }
 
 PropertyMap UniqueFileIdentifierFrame::asProperties() const
diff --git a/taglib/mpeg/id3v2/frames/unknownframe.cpp b/taglib/mpeg/id3v2/frames/unknownframe.cpp
index 4def028b..9d059193 100644
--- a/taglib/mpeg/id3v2/frames/unknownframe.cpp
+++ b/taglib/mpeg/id3v2/frames/unknownframe.cpp
@@ -51,7 +51,7 @@ UnknownFrame::~UnknownFrame()
 
 String UnknownFrame::toString() const
 {
-  return String::null;
+  return String();
 }
 
 ByteVector UnknownFrame::data() const
diff --git a/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp b/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp
index 8f96cb8d..f97cdc5a 100644
--- a/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp
+++ b/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp
@@ -119,8 +119,6 @@ PropertyMap UnsynchronizedLyricsFrame::asProperties() const
   String key = description().upper();
   if(key.isEmpty() || key.upper() == "LYRICS")
     map.insert("LYRICS", text());
-  else if(key.isNull())
-    map.unsupportedData().append(L"USLT/" + description());
   else
     map.insert("LYRICS:" + key, text());
   return map;
@@ -164,7 +162,7 @@ void UnsynchronizedLyricsFrame::parseFields(const ByteVector &data)
     } else {
       d->description = String(l.front(), d->textEncoding);
       d->text = String(l.back(), d->textEncoding);
-    }  
+    }
   }
 }
 
diff --git a/taglib/mpeg/id3v2/frames/urllinkframe.cpp b/taglib/mpeg/id3v2/frames/urllinkframe.cpp
index 5bf48d5a..7852d103 100644
--- a/taglib/mpeg/id3v2/frames/urllinkframe.cpp
+++ b/taglib/mpeg/id3v2/frames/urllinkframe.cpp
@@ -159,8 +159,6 @@ PropertyMap UserUrlLinkFrame::asProperties() const
   String key = description().upper();
   if(key.isEmpty() || key.upper() == "URL")
     map.insert("URL", url());
-  else if(key.isNull())
-    map.unsupportedData().append(L"WXXX/" + description());
   else
     map.insert("URL:" + key, url());
   return map;
diff --git a/taglib/mpeg/id3v2/id3v2frame.cpp b/taglib/mpeg/id3v2/id3v2frame.cpp
index a30501a5..bffd2550 100644
--- a/taglib/mpeg/id3v2/id3v2frame.cpp
+++ b/taglib/mpeg/id3v2/id3v2frame.cpp
@@ -311,7 +311,7 @@ String Frame::readStringField(const ByteVector &data, String::Type encoding, siz
 
   const size_t end = data.find(delimiter, position, delimiter.size());
   if(end == ByteVector::npos() || end < position)
-    return String::null;
+    return String();
 
   String str;
   if(encoding == String::Latin1)
diff --git a/taglib/mpeg/id3v2/id3v2framefactory.cpp b/taglib/mpeg/id3v2/id3v2framefactory.cpp
index 44da49c1..4c5d3af8 100644
--- a/taglib/mpeg/id3v2/id3v2framefactory.cpp
+++ b/taglib/mpeg/id3v2/id3v2framefactory.cpp
@@ -504,7 +504,7 @@ void FrameFactory::updateGenre(TextIdentificationFrame *frame) const
   }
 
   if(newfields.isEmpty())
-    fields.append(String::null);
+    fields.append(String());
 
   frame->setText(newfields);
 
diff --git a/taglib/mpeg/id3v2/id3v2tag.cpp b/taglib/mpeg/id3v2/id3v2tag.cpp
index 96ed8d02..dd32f2c7 100644
--- a/taglib/mpeg/id3v2/id3v2tag.cpp
+++ b/taglib/mpeg/id3v2/id3v2tag.cpp
@@ -139,21 +139,21 @@ String ID3v2::Tag::title() const
 {
   if(!d->frameListMap["TIT2"].isEmpty())
     return d->frameListMap["TIT2"].front()->toString();
-  return String::null;
+  return String();
 }
 
 String ID3v2::Tag::artist() const
 {
   if(!d->frameListMap["TPE1"].isEmpty())
     return d->frameListMap["TPE1"].front()->toString();
-  return String::null;
+  return String();
 }
 
 String ID3v2::Tag::album() const
 {
   if(!d->frameListMap["TALB"].isEmpty())
     return d->frameListMap["TALB"].front()->toString();
-  return String::null;
+  return String();
 }
 
 String ID3v2::Tag::comment() const
@@ -161,7 +161,7 @@ String ID3v2::Tag::comment() const
   const FrameList &comments = d->frameListMap["COMM"];
 
   if(comments.isEmpty())
-    return String::null;
+    return String();
 
   for(FrameList::ConstIterator it = comments.begin(); it != comments.end(); ++it)
   {
@@ -183,7 +183,7 @@ String ID3v2::Tag::genre() const
   if(d->frameListMap["TCON"].isEmpty() ||
      !dynamic_cast<TextIdentificationFrame *>(d->frameListMap["TCON"].front()))
   {
-    return String::null;
+    return String();
   }
 
   // ID3v2.4 lists genres as the fields in its frames field list.  If the field
diff --git a/taglib/ogg/xiphcomment.cpp b/taglib/ogg/xiphcomment.cpp
index 64e05ac0..daf8181e 100644
--- a/taglib/ogg/xiphcomment.cpp
+++ b/taglib/ogg/xiphcomment.cpp
@@ -62,21 +62,21 @@ Ogg::XiphComment::~XiphComment()
 String Ogg::XiphComment::title() const
 {
   if(d->fieldListMap["TITLE"].isEmpty())
-    return String::null;
+    return String();
   return d->fieldListMap["TITLE"].toString();
 }
 
 String Ogg::XiphComment::artist() const
 {
   if(d->fieldListMap["ARTIST"].isEmpty())
-    return String::null;
+    return String();
   return d->fieldListMap["ARTIST"].toString();
 }
 
 String Ogg::XiphComment::album() const
 {
   if(d->fieldListMap["ALBUM"].isEmpty())
-    return String::null;
+    return String();
   return d->fieldListMap["ALBUM"].toString();
 }
 
@@ -92,13 +92,13 @@ String Ogg::XiphComment::comment() const
     return d->fieldListMap["COMMENT"].toString();
   }
 
-  return String::null;
+  return String();
 }
 
 String Ogg::XiphComment::genre() const
 {
   if(d->fieldListMap["GENRE"].isEmpty())
-    return String::null;
+    return String();
   return d->fieldListMap["GENRE"].toString();
 }
 
@@ -137,7 +137,14 @@ void Ogg::XiphComment::setAlbum(const String &s)
 
 void Ogg::XiphComment::setComment(const String &s)
 {
-  addField(d->commentField.isEmpty() ? "DESCRIPTION" : d->commentField, s);
+  if(d->commentField.isEmpty()) {
+    if(!d->fieldListMap["DESCRIPTION"].isEmpty())
+      d->commentField = "DESCRIPTION";
+    else
+      d->commentField = "COMMENT";
+  }
+
+  addField(d->commentField, s);
 }
 
 void Ogg::XiphComment::setGenre(const String &s)
diff --git a/taglib/s3m/s3mfile.cpp b/taglib/s3m/s3mfile.cpp
index dbd6654f..61a2d1d8 100644
--- a/taglib/s3m/s3mfile.cpp
+++ b/taglib/s3m/s3mfile.cpp
@@ -124,7 +124,7 @@ bool S3M::File::save()
     if(i < lines.size())
       writeString(lines[i], 27);
     else
-      writeString(String::null, 27);
+      writeString(String(), 27);
     // string terminating NUL is not optional:
     writeByte(0);
   }
diff --git a/taglib/tag.cpp b/taglib/tag.cpp
index f4447a49..e4f5c933 100644
--- a/taglib/tag.cpp
+++ b/taglib/tag.cpp
@@ -58,15 +58,15 @@ bool Tag::isEmpty() const
 PropertyMap Tag::properties() const
 {
   PropertyMap map;
-  if(!(title().isNull()))
+  if(!(title().isEmpty()))
     map["TITLE"].append(title());
-  if(!(artist().isNull()))
+  if(!(artist().isEmpty()))
     map["ARTIST"].append(artist());
-  if(!(album().isNull()))
+  if(!(album().isEmpty()))
     map["ALBUM"].append(album());
-  if(!(comment().isNull()))
+  if(!(comment().isEmpty()))
     map["COMMENT"].append(comment());
-  if(!(genre().isNull()))
+  if(!(genre().isEmpty()))
     map["GENRE"].append(genre());
   if(!(year() == 0))
     map["DATE"].append(String::number(year()));
@@ -89,31 +89,31 @@ PropertyMap Tag::setProperties(const PropertyMap &origProps)
     setTitle(properties["TITLE"].front());
     oneValueSet.append("TITLE");
   } else
-    setTitle(String::null);
+    setTitle(String());
 
   if(properties.contains("ARTIST")) {
     setArtist(properties["ARTIST"].front());
     oneValueSet.append("ARTIST");
   } else
-    setArtist(String::null);
+    setArtist(String());
 
   if(properties.contains("ALBUM")) {
     setAlbum(properties["ALBUM"].front());
     oneValueSet.append("ALBUM");
   } else
-    setAlbum(String::null);
+    setAlbum(String());
 
   if(properties.contains("COMMENT")) {
     setComment(properties["COMMENT"].front());
     oneValueSet.append("COMMENT");
   } else
-    setComment(String::null);
+    setComment(String());
 
   if(properties.contains("GENRE")) {
     setGenre(properties["GENRE"].front());
     oneValueSet.append("GENRE");
   } else
-    setGenre(String::null);
+    setGenre(String());
 
   if(properties.contains("DATE")) {
     bool ok;
diff --git a/taglib/tagunion.cpp b/taglib/tagunion.cpp
index c47bc2c8..78cc62af 100644
--- a/taglib/tagunion.cpp
+++ b/taglib/tagunion.cpp
@@ -23,10 +23,10 @@
  *   http://www.mozilla.org/MPL/                                           *
  ***************************************************************************/
 
-#include "tagunion.h"
-#include "tstringlist.h"
-#include "tpropertymap.h"
-#include "tsmartptr.h"
+#include <tagunion.h>
+#include <tstringlist.h>
+#include <tpropertymap.h>
+#include <tsmartptr.h>
 
 #define stringUnion(method)                                               \
   for(size_t j = 0; j < COUNT; ++j) {                                     \
@@ -34,7 +34,7 @@
     if(!val.isEmpty())                                                    \
       return val;                                                         \
   }                                                                       \
-  return String::null;
+  return String();
 
 #define numberUnion(method)                                               \
   for(size_t j = 0; j < COUNT; ++j) {                                     \
diff --git a/taglib/tagutils.cpp b/taglib/tagutils.cpp
new file mode 100644
index 00000000..2c556ca7
--- /dev/null
+++ b/taglib/tagutils.cpp
@@ -0,0 +1,79 @@
+/***************************************************************************
+    copyright            : (C) 2015 by Tsuda Kageyu
+    email                : tsuda.kageyu@gmail.com
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include <tfile.h>
+
+#include "id3v1tag.h"
+#include "id3v2header.h"
+#include "apetag.h"
+
+#include "tagutils.h"
+
+using namespace TagLib;
+
+offset_t Utils::findID3v1(File *file)
+{
+  if(!file->isValid())
+    return -1;
+
+  file->seek(-128, File::End);
+  const offset_t p = file->tell();
+
+  if(file->readBlock(3) == ID3v1::Tag::fileIdentifier())
+    return p;
+
+  return -1;
+}
+
+offset_t Utils::findID3v2(File *file)
+{
+  if(!file->isValid())
+    return -1;
+
+  file->seek(0);
+
+  if(file->readBlock(3) == ID3v2::Header::fileIdentifier())
+    return 0;
+
+  return -1;
+}
+
+offset_t Utils::findAPE(File *file, offset_t id3v1Location)
+{
+  if(!file->isValid())
+    return -1;
+
+  if(id3v1Location >= 0)
+    file->seek(id3v1Location - 32, File::Beginning);
+  else
+    file->seek(-32, File::End);
+
+  const offset_t p = file->tell();
+
+  if(file->readBlock(8) == APE::Tag::fileIdentifier())
+    return p;
+
+  return -1;
+}
diff --git a/taglib/tagutils.h b/taglib/tagutils.h
new file mode 100644
index 00000000..0001f34b
--- /dev/null
+++ b/taglib/tagutils.h
@@ -0,0 +1,49 @@
+/***************************************************************************
+    copyright            : (C) 2015 by Tsuda Kageyu
+    email                : tsuda.kageyu@gmail.com
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_TAGUTILS_H
+#define TAGLIB_TAGUTILS_H
+
+// THIS FILE IS NOT A PART OF THE TAGLIB API
+
+#ifndef DO_NOT_DOCUMENT  // tell Doxygen not to document this header
+
+namespace TagLib {
+
+  class File;
+
+  namespace Utils {
+
+    offset_t findID3v1(File *file);
+
+    offset_t findID3v2(File *file);
+
+    offset_t findAPE(File *file, offset_t id3v1Location);
+  }
+}
+
+#endif
+
+#endif
diff --git a/taglib/toolkit/tiostream.cpp b/taglib/toolkit/tiostream.cpp
index 80570cab..6c4c1b51 100644
--- a/taglib/toolkit/tiostream.cpp
+++ b/taglib/toolkit/tiostream.cpp
@@ -147,7 +147,7 @@ String FileName::toString() const
   else if(!d->data->name.empty()) {
     const int len = ::MultiByteToWideChar(CP_ACP, 0, d->data->name.c_str(), -1, NULL, 0);
     if(len == 0)
-      return String::null;
+      return String();
 
     std::vector<wchar_t> buf(len);
     ::MultiByteToWideChar(CP_ACP, 0, d->data->name.c_str(), -1, &buf[0], len);
@@ -155,7 +155,7 @@ String FileName::toString() const
     return String(&buf[0]);
   }
   else {
-    return String::null;
+    return String();
   }
 }
 
diff --git a/taglib/toolkit/tpropertymap.cpp b/taglib/toolkit/tpropertymap.cpp
index 313d7fb4..1c6a47d9 100644
--- a/taglib/toolkit/tpropertymap.cpp
+++ b/taglib/toolkit/tpropertymap.cpp
@@ -35,7 +35,7 @@ PropertyMap::PropertyMap(const SimplePropertyMap &m)
 {
   for(SimplePropertyMap::ConstIterator it = m.begin(); it != m.end(); ++it){
     String key = it->first.upper();
-    if(!key.isNull())
+    if(!key.isEmpty())
       insert(it->first, it->second);
     else
       unsupported.append(it->first);
@@ -144,7 +144,8 @@ bool PropertyMap::operator!=(const PropertyMap &other) const
 
 String PropertyMap::toString() const
 {
-  String ret = "";
+  String ret;
+
   for(ConstIterator it = begin(); it != end(); ++it)
     ret += it->first+"="+it->second.toString(", ") + "\n";
   if(!unsupported.isEmpty())
diff --git a/taglib/trueaudio/trueaudiofile.cpp b/taglib/trueaudio/trueaudiofile.cpp
index a070f536..508d3a59 100644
--- a/taglib/trueaudio/trueaudiofile.cpp
+++ b/taglib/trueaudio/trueaudiofile.cpp
@@ -33,6 +33,7 @@
 #include <tagunion.h>
 #include <tstringlist.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include "trueaudiofile.h"
 #include "id3v1tag.h"
@@ -240,7 +241,7 @@ void TrueAudio::File::read(bool readProperties)
 {
   // Look for an ID3v2 tag
 
-  d->ID3v2Location = findID3v2();
+  d->ID3v2Location = Utils::findID3v2(this);
 
   if(d->ID3v2Location >= 0) {
 
@@ -256,7 +257,7 @@ void TrueAudio::File::read(bool readProperties)
 
   // Look for an ID3v1 tag
 
-  d->ID3v1Location = findID3v1();
+  d->ID3v1Location = Utils::findID3v1(this);
 
   if(d->ID3v1Location >= 0) {
     d->tag.set(TrueAudioID3v1Index, new ID3v1::Tag(this, d->ID3v1Location));
@@ -288,30 +289,3 @@ void TrueAudio::File::read(bool readProperties)
     d->properties = new AudioProperties(readBlock(HeaderSize), streamLength);
   }
 }
-
-offset_t TrueAudio::File::findID3v1()
-{
-  if(!isValid())
-    return -1;
-
-  seek(-128, End);
-  offset_t p = tell();
-
-  if(readBlock(3) == ID3v1::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
-
-offset_t TrueAudio::File::findID3v2()
-{
-  if(!isValid())
-    return -1;
-
-  seek(0);
-
-  if(readBlock(3) == ID3v2::Header::fileIdentifier())
-    return 0;
-
-  return -1;
-}
diff --git a/taglib/trueaudio/trueaudiofile.h b/taglib/trueaudio/trueaudiofile.h
index 70e66b04..1ea5790d 100644
--- a/taglib/trueaudio/trueaudiofile.h
+++ b/taglib/trueaudio/trueaudiofile.h
@@ -231,8 +231,6 @@ namespace TagLib {
       File &operator=(const File &);
 
       void read(bool readProperties);
-      offset_t findID3v1();
-      offset_t findID3v2();
 
       class FilePrivate;
       FilePrivate *d;
diff --git a/taglib/wavpack/wavpackfile.cpp b/taglib/wavpack/wavpackfile.cpp
index abc67917..2411ef08 100644
--- a/taglib/wavpack/wavpackfile.cpp
+++ b/taglib/wavpack/wavpackfile.cpp
@@ -32,6 +32,7 @@
 #include <tdebug.h>
 #include <tagunion.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include "wavpackfile.h"
 #include "id3v1tag.h"
@@ -233,7 +234,7 @@ void WavPack::File::read(bool readProperties)
 {
   // Look for an ID3v1 tag
 
-  d->ID3v1Location = findID3v1();
+  d->ID3v1Location = Utils::findID3v1(this);
 
   if(d->ID3v1Location >= 0) {
     d->tag.set(WavID3v1Index, new ID3v1::Tag(this, d->ID3v1Location));
@@ -242,7 +243,7 @@ void WavPack::File::read(bool readProperties)
 
   // Look for an APE tag
 
-  d->APELocation = findAPE();
+  d->APELocation = Utils::findAPE(this, d->ID3v1Location);
 
   if(d->APELocation >= 0) {
     d->tag.set(WavAPEIndex, new APE::Tag(this, d->APELocation));
@@ -270,35 +271,3 @@ void WavPack::File::read(bool readProperties)
     d->properties = new AudioProperties(this, streamLength);
   }
 }
-
-offset_t WavPack::File::findAPE()
-{
-  if(!isValid())
-    return -1;
-
-  if(d->hasID3v1)
-    seek(-160, End);
-  else
-    seek(-32, End);
-
-  offset_t p = tell();
-
-  if(readBlock(8) == APE::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
-
-offset_t WavPack::File::findID3v1()
-{
-  if(!isValid())
-    return -1;
-
-  seek(-128, End);
-  offset_t p = tell();
-
-  if(readBlock(3) == ID3v1::Tag::fileIdentifier())
-    return p;
-
-  return -1;
-}
diff --git a/taglib/wavpack/wavpackfile.h b/taglib/wavpack/wavpackfile.h
index ebed7a9d..88a83d0a 100644
--- a/taglib/wavpack/wavpackfile.h
+++ b/taglib/wavpack/wavpackfile.h
@@ -199,8 +199,6 @@ namespace TagLib {
       File &operator=(const File &);
 
       void read(bool readProperties);
-      offset_t findID3v1();
-      offset_t findAPE();
 
       class FilePrivate;
       FilePrivate *d;
diff --git a/taglib/xm/xmfile.cpp b/taglib/xm/xmfile.cpp
index 9cff50d5..01ccd5af 100644
--- a/taglib/xm/xmfile.cpp
+++ b/taglib/xm/xmfile.cpp
@@ -452,7 +452,7 @@ bool XM::File::save()
     seek(pos + 4);
     const uint len = std::min(22U, instrumentHeaderSize - 4U);
     if(i >= lines.size())
-      writeString(String::null, len);
+      writeString(String(), len);
     else
       writeString(lines[i], len);
 
@@ -483,7 +483,7 @@ bool XM::File::save()
           seek(pos + 18);
           const uint len = std::min(sampleHeaderSize - 18U, 22U);
           if(sampleNameIndex >= lines.size())
-            writeString(String::null, len);
+            writeString(String(), len);
           else
             writeString(lines[sampleNameIndex ++], len);
         }
diff --git a/tests/test_apetag.cpp b/tests/test_apetag.cpp
index 72893c5b..3a4d853b 100644
--- a/tests/test_apetag.cpp
+++ b/tests/test_apetag.cpp
@@ -108,7 +108,7 @@ public:
     ByteVector data("Test Data");
     item.setBinaryData(data);
     CPPUNIT_ASSERT(item.values().isEmpty());
-    CPPUNIT_ASSERT_EQUAL(String::null, item.toString());
+    CPPUNIT_ASSERT_EQUAL(String(), item.toString());
     CPPUNIT_ASSERT_EQUAL(data, item.binaryData());
 
     item.setValue("Test Text 2");
diff --git a/tests/test_fileref.cpp b/tests/test_fileref.cpp
index cda44153..1e28d48f 100644
--- a/tests/test_fileref.cpp
+++ b/tests/test_fileref.cpp
@@ -4,12 +4,26 @@
 #include <fileref.h>
 #include <oggflacfile.h>
 #include <vorbisfile.h>
+#include <mpegfile.h>
 #include <cppunit/extensions/HelperMacros.h>
 #include "utils.h"
+#include <tfilestream.h>
 
 using namespace std;
 using namespace TagLib;
 
+namespace
+{
+  class DummyResolver : public FileRef::FileTypeResolver
+  {
+  public:
+    virtual File *createFile(FileName fileName, bool, AudioProperties::ReadStyle) const
+    {
+      return new Ogg::Vorbis::File(fileName);
+    }
+  };
+}
+
 class TestFileRef : public CppUnit::TestFixture
 {
   CPPUNIT_TEST_SUITE(TestFileRef);
@@ -30,6 +44,7 @@ class TestFileRef : public CppUnit::TestFixture
   CPPUNIT_TEST(testAIFF);
   CPPUNIT_TEST(testAIFC);
   CPPUNIT_TEST(testUnsupported);
+  CPPUNIT_TEST(testFileResolver);
   CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -80,26 +95,16 @@ public:
     CPPUNIT_ASSERT_EQUAL(f->tag()->year(), TagLib::uint(2080));
     delete f;
 
-    f = new FileRef(newname.c_str());
-    CPPUNIT_ASSERT(f->isValid());
+    FileStream fs(newname.c_str());
+    f = new FileRef(&fs);
     CPPUNIT_ASSERT(!f->isNull());
-    PropertyMap prop = f->properties();
-    CPPUNIT_ASSERT_EQUAL(prop["ARTIST"].front(), String("ttest artist"));
-    CPPUNIT_ASSERT_EQUAL(prop["TITLE" ].front(), String("ytest title"));
-    prop["ARTIST"].front() = "a test artist";
-    prop["TITLE" ].front() = "b test title";
-    f->setProperties(prop);
-    f->save();
+    CPPUNIT_ASSERT_EQUAL(f->tag()->artist(), String("ttest artist"));
+    CPPUNIT_ASSERT_EQUAL(f->tag()->title(), String("ytest title"));
+    CPPUNIT_ASSERT_EQUAL(f->tag()->genre(), String("uTest!"));
+    CPPUNIT_ASSERT_EQUAL(f->tag()->album(), String("ialbummmm"));
+    CPPUNIT_ASSERT_EQUAL(f->tag()->track(), TagLib::uint(7));
+    CPPUNIT_ASSERT_EQUAL(f->tag()->year(), TagLib::uint(2080));
     delete f;
-    
-    f = new FileRef(newname.c_str());
-    CPPUNIT_ASSERT(f->isValid());
-    CPPUNIT_ASSERT(!f->isNull());
-    prop = f->properties();
-    CPPUNIT_ASSERT_EQUAL(prop["ARTIST"].front(), String("a test artist"));
-    CPPUNIT_ASSERT_EQUAL(prop["TITLE" ].front(), String("b test title"));
-    delete f;
-    
   }
 
   void testMusepack()
@@ -192,10 +197,25 @@ public:
   {
     FileRef f1(TEST_FILE_PATH_C("no-extension"));
     CPPUNIT_ASSERT(f1.isNull());
-    
+
     FileRef f2(TEST_FILE_PATH_C("unsupported-extension.xxx"));
     CPPUNIT_ASSERT(f2.isNull());
   }
+
+  void testFileResolver()
+  {
+    FileRef *f = new FileRef(TEST_FILE_PATH_C("xing.mp3"));
+    CPPUNIT_ASSERT(dynamic_cast<MPEG::File *>(f->file()) != NULL);
+    delete f;
+
+    DummyResolver resolver;
+    FileRef::addFileTypeResolver(&resolver);
+
+    f = new FileRef(TEST_FILE_PATH_C("xing.mp3"));
+    CPPUNIT_ASSERT(dynamic_cast<Ogg::Vorbis::File *>(f->file()) != NULL);
+    delete f;
+  }
+
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(TestFileRef);
diff --git a/tests/test_id3v2.cpp b/tests/test_id3v2.cpp
index 8e885541..0f8d0ac8 100644
--- a/tests/test_id3v2.cpp
+++ b/tests/test_id3v2.cpp
@@ -38,7 +38,7 @@ class PublicFrame : public ID3v2::Frame
       size_t position = 0;
       return ID3v2::Frame::readStringField(data, encoding, position);
     }
-    virtual String toString() const { return String::null; }
+    virtual String toString() const { return String(); }
     virtual void parseFields(const ByteVector &) {}
     virtual ByteVector renderFields() const { return ByteVector(); }
 };
diff --git a/tests/test_it.cpp b/tests/test_it.cpp
index 68fd67b1..c5d16326 100644
--- a/tests/test_it.cpp
+++ b/tests/test_it.cpp
@@ -123,10 +123,10 @@ private:
     CPPUNIT_ASSERT_EQUAL((TagLib::uchar)128, p->panningSeparation());
     CPPUNIT_ASSERT_EQUAL((TagLib::uchar)  0, p->pitchWheelDepth());
     CPPUNIT_ASSERT_EQUAL(title, t->title());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->artist());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->album());
+    CPPUNIT_ASSERT_EQUAL(String(), t->artist());
+    CPPUNIT_ASSERT_EQUAL(String(), t->album());
     CPPUNIT_ASSERT_EQUAL(comment, t->comment());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->genre());
+    CPPUNIT_ASSERT_EQUAL(String(), t->genre());
     CPPUNIT_ASSERT_EQUAL(0U, t->year());
     CPPUNIT_ASSERT_EQUAL(0U, t->track());
     CPPUNIT_ASSERT_EQUAL(String("Impulse Tracker"), t->trackerName());
diff --git a/tests/test_mod.cpp b/tests/test_mod.cpp
index 9120de91..e776d5a3 100644
--- a/tests/test_mod.cpp
+++ b/tests/test_mod.cpp
@@ -113,10 +113,10 @@ private:
     CPPUNIT_ASSERT_EQUAL(31U, p->instrumentCount());
     CPPUNIT_ASSERT_EQUAL((uchar)1, p->lengthInPatterns());
     CPPUNIT_ASSERT_EQUAL(title, t->title());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->artist());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->album());
+    CPPUNIT_ASSERT_EQUAL(String(), t->artist());
+    CPPUNIT_ASSERT_EQUAL(String(), t->album());
     CPPUNIT_ASSERT_EQUAL(comment, t->comment());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->genre());
+    CPPUNIT_ASSERT_EQUAL(String(), t->genre());
     CPPUNIT_ASSERT_EQUAL(0U, t->year());
     CPPUNIT_ASSERT_EQUAL(0U, t->track());
     CPPUNIT_ASSERT_EQUAL(String("StarTrekker"), t->trackerName());
diff --git a/tests/test_s3m.cpp b/tests/test_s3m.cpp
index 2b289ece..bbc0d0f9 100644
--- a/tests/test_s3m.cpp
+++ b/tests/test_s3m.cpp
@@ -110,10 +110,10 @@ private:
     CPPUNIT_ASSERT_EQUAL((TagLib::uchar)125, p->tempo());
     CPPUNIT_ASSERT_EQUAL((TagLib::uchar)  6, p->bpmSpeed());
     CPPUNIT_ASSERT_EQUAL(title, t->title());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->artist());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->album());
+    CPPUNIT_ASSERT_EQUAL(String(), t->artist());
+    CPPUNIT_ASSERT_EQUAL(String(), t->album());
     CPPUNIT_ASSERT_EQUAL(comment, t->comment());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->genre());
+    CPPUNIT_ASSERT_EQUAL(String(), t->genre());
     CPPUNIT_ASSERT_EQUAL(0U, t->year());
     CPPUNIT_ASSERT_EQUAL(0U, t->track());
     CPPUNIT_ASSERT_EQUAL(String("ScreamTracker III"), t->trackerName());
diff --git a/tests/test_string.cpp b/tests/test_string.cpp
index 5afc32e5..32137cfe 100644
--- a/tests/test_string.cpp
+++ b/tests/test_string.cpp
@@ -75,7 +75,7 @@ public:
 
     s.clear();
     CPPUNIT_ASSERT(s.isEmpty());
-    CPPUNIT_ASSERT(!s.isNull());
+    CPPUNIT_ASSERT(!s.isNull()); // deprecated, but still worth it to check.
 
     String unicode("José Carlos", String::UTF8);
     CPPUNIT_ASSERT(strcmp(unicode.toCString(), "Jos\xe9 Carlos") == 0);
diff --git a/tests/test_xiphcomment.cpp b/tests/test_xiphcomment.cpp
index 897bbac0..00ae4f56 100644
--- a/tests/test_xiphcomment.cpp
+++ b/tests/test_xiphcomment.cpp
@@ -1,5 +1,6 @@
 #include <string>
 #include <stdio.h>
+#include <flacfile.h>
 #include <xiphcomment.h>
 #include <tpropertymap.h>
 #include <tdebug.h>
@@ -17,6 +18,7 @@ class TestXiphComment : public CppUnit::TestFixture
   CPPUNIT_TEST(testTrack);
   CPPUNIT_TEST(testSetTrack);
   CPPUNIT_TEST(testInvalidKeys);
+  CPPUNIT_TEST(testClearComment);
   CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -74,6 +76,22 @@ public:
     CPPUNIT_ASSERT(cmt.properties().isEmpty());
   }
 
+  void testClearComment()
+  {
+    ScopedFileCopy copy("no-tags", ".flac");
+
+    {
+      FLAC::File f(copy.fileName().c_str());
+      f.xiphComment()->addField("COMMENT", "Comment1");
+      f.save();
+    }
+    {
+      FLAC::File f(copy.fileName().c_str());
+      f.xiphComment()->setComment("");
+      CPPUNIT_ASSERT_EQUAL(String(""), f.xiphComment()->comment());
+    }
+  }
+
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(TestXiphComment);
diff --git a/tests/test_xm.cpp b/tests/test_xm.cpp
index a9a91d7f..6929e5ba 100644
--- a/tests/test_xm.cpp
+++ b/tests/test_xm.cpp
@@ -139,13 +139,13 @@ public:
     CPPUNIT_ASSERT_EQUAL((TagLib::ushort)  6, p->tempo());
     CPPUNIT_ASSERT_EQUAL((TagLib::ushort)125, p->bpmSpeed());
     CPPUNIT_ASSERT_EQUAL(titleBefore, t->title());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->artist());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->album());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->comment());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->genre());
+    CPPUNIT_ASSERT_EQUAL(String(), t->artist());
+    CPPUNIT_ASSERT_EQUAL(String(), t->album());
+    CPPUNIT_ASSERT_EQUAL(String(), t->comment());
+    CPPUNIT_ASSERT_EQUAL(String(), t->genre());
     CPPUNIT_ASSERT_EQUAL(0U, t->year());
     CPPUNIT_ASSERT_EQUAL(0U, t->track());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->trackerName());
+    CPPUNIT_ASSERT_EQUAL(String(), t->trackerName());
   }
 
   void testWriteTagsShort()
@@ -185,10 +185,10 @@ private:
     CPPUNIT_ASSERT_EQUAL((TagLib::ushort)  6, p->tempo());
     CPPUNIT_ASSERT_EQUAL((TagLib::ushort)125, p->bpmSpeed());
     CPPUNIT_ASSERT_EQUAL(title, t->title());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->artist());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->album());
+    CPPUNIT_ASSERT_EQUAL(String(), t->artist());
+    CPPUNIT_ASSERT_EQUAL(String(), t->album());
     CPPUNIT_ASSERT_EQUAL(comment, t->comment());
-    CPPUNIT_ASSERT_EQUAL(String::null, t->genre());
+    CPPUNIT_ASSERT_EQUAL(String(), t->genre());
     CPPUNIT_ASSERT_EQUAL(0U, t->year());
     CPPUNIT_ASSERT_EQUAL(0U, t->track());
     CPPUNIT_ASSERT_EQUAL(trackerName, t->trackerName());