Avoid using String::null where an empty string is required.

String::null is not necessarily be empty or remains the same instance.
Using it in a public header may lead to a linkage error.

taglib/mpeg/id3v1/id3v1tag.cpp

@@ -184,7 +184,7 @@ 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)

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

taglib/mpeg/id3v2/frames/textidentificationframe.cpp

@@ -312,8 +312,8 @@ 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);
 }
 
@@ -341,7 +341,7 @@ String UserTextIdentificationFrame::description() const
 {
   return !TextIdentificationFrame::fieldList().isEmpty()
     ? TextIdentificationFrame::fieldList().front()
-    : String::null;
+    : String();
 }
 
 StringList UserTextIdentificationFrame::fieldList() const
@@ -354,7 +354,7 @@ StringList UserTextIdentificationFrame::fieldList() const
 void UserTextIdentificationFrame::setText(const String &text)
 {
   if(description().isEmpty())
-    setDescription(String::null);
+    setDescription(String());
 
   TextIdentificationFrame::setText(StringList(description()).append(text));
 }
@@ -362,7 +362,7 @@ 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));
 }
@@ -417,7 +417,7 @@ void UserTextIdentificationFrame::checkFields()
   int fields = fieldList().size();
 
   if(fields == 0)
-    setDescription(String::null);
+    setDescription(String());
   if(fields <= 1)
-    setText(String::null);
+    setText(String());
 }

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

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

taglib/mpeg/id3v2/id3v2frame.cpp

@@ -317,7 +317,7 @@ String Frame::readStringField(const ByteVector &data, String::Type encoding, int
   int end = data.find(delimiter, *position, delimiter.size());
 
   if(end < *position)
-    return String::null;
+    return String();
 
   String str;
   if(encoding == String::Latin1)

taglib/mpeg/id3v2/id3v2framefactory.cpp

@@ -516,7 +516,7 @@ void FrameFactory::updateGenre(TextIdentificationFrame *frame) const
   }
 
   if(newfields.isEmpty())
-    fields.append(String::null);
+    fields.append(String());
 
   frame->setText(newfields);
 

taglib/mpeg/id3v2/id3v2tag.cpp

@@ -140,21 +140,21 @@ 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
@@ -162,7 +162,7 @@ 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)
   {
@@ -184,7 +184,7 @@ 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