While building gstreamer 0.11.0 on the Open Build Service (*target openSUSE Factory/12.1), The build aborts with:

I: Program returns random data in a function
E: gstreamer-plugins-base no-return-in-nonvoid-function gstxmptag.c:178

The raised compiler warning from the build log is:
gstxmptag.c: In function 'xmp_tag_type_get_name':
gstxmptag.c:178:1: warning: control reaches end of non-void function [-Wreturn-type]

The code fragment in question:
static const gchar *
xmp_tag_type_get_name (GstXmpTagType tagtype)
{
  switch (tagtype) {
    case GstXmpTagTypeSeq:
      return "rdf:Seq";
    case GstXmpTagTypeBag:
      return "rdf:Bag";
    default:
      g_assert_not_reached ();
  }
}

==> Thus: the 'default' path does not have a return value for the function. I assume returning NULL might be safe/sufficient?