Realisation problems with semantically null modifiers

It is possible to send the OpenCCG realiser into an infinite loop, if you use semantically empty modifier categories. One of our NLG students tried to handle the commas in non-restrictive relative clauses as NP postmodifiers:

  Giovanni's      ,           which       rocks          , 
  ----------  --------  ----------------  ----------  -------
     NPx      NPx\NPx   NPx\NPx/(Se\NPx)  Se\NPx      NPx\NPx
   @x Gio's                               @e rock
  -------------------<                    @e  x
    NPx : @x Gio's      --------------------------->
                        NPx\NPx : @e rock,@e  x
  -------------------------------------------------<
          NPx : @e rock, @e  x, @x Gio's

Unfortunately, these semantically null post-modifiers bamboozle the realiser:

[Is this the same for premodifiers?]