Removed calls to allow 'None' as product of catalysis
Removed calls to allow 'None' as product of catalysis

d-fan/pysb,alubbock/pysb,neurord/pysb,spgarbet/pysb,spgarbet/pysb,pysb/pysb,d-fan/pysb,johnbachman/pysb,neurord/pysb,d-fan/pysb,spgarbet/pysb,neurord/pysb,LoLab-VU/pysb,LoLab-VU/pysb,jmuhlich/pysb,johnbachman/pysb