title: Setting Explicit tag for Apple .m4a file with TagLib#
body: <p>I'm using this method to add the <code>ITUNESADVISORY</code> tag:</p>
  
  <pre><code>static void SetExplicit(string file)
  {
      var f = TagLib.File.Create(file);
      TagLib.Mpeg4.AppleTag customTag = (TagLib.Mpeg4.AppleTag)f.GetTag(TagLib.TagTypes.Apple, true);
      var vector = new TagLib.ByteVector();
      vector.Add((byte)1);
      customTag.SetData("ITUNESADVISORY", vector, (int)TagLib.Mpeg4.AppleDataBox.FlagType.ContainsData);
      f.Save();
  }
  </code></pre>
  
  <p>Except it doesn't work. It throws and exception (<code>type</code> cannot be <code>null</code>) on the <code>SetData(type, vector, flags)</code> line. Do I need to somehow add the DataBox first, or something?</p>
  
  <p>Thanks!</p>