Adding the new attributes for showing a lack of detected cds and mrna end

modules/Bio/EnsEMBL/Utils/IO/GTFSerializer.pm

@@ -428,6 +428,15 @@ sub _print_attribs {
     print $fh qq{ tag "seleno";};
   }
 
+  if($transcript && $transcript->isa('Bio::EnsEMBL::Transcript')) {
+    foreach my $tag (qw/cds_end_NF cds_start_NF mRNA_end_NF mRNA_start_NF/) {
+      my $attributes = $transcript->get_all_Attributes($tag);
+      if(@{$attributes}) {
+        print $fh qq{ tag "${tag}";};
+      }
+    }
+  }
+
   return;
 } ## end sub _print_attribs