The RIB parser could be more picky on empty arguments. They are contained in the
SubidivsionMesh calls in the two example subd RIBs before "P"is defined. PRMan issues an error on
these, AQSIS does not.
Empty arguments ('') in the bytestream would mean that the original argument passed to the 'Ri'
call was RI_NULL. But according to the spec, RI_NULL is just the end delimiter to the token-value
list. Neither is it written to the RIB nor can any token-value pairs appear after it in the 'Ri*' call.