LoLab-VU/pysb — pull request #1 by d-fan (2013-08-30 17:29:07+00:00)
Title: Allow 'None' to be passed as arguments for 'catalyze_one_step' and 'catalyze_one_step_reversible'

Passing 'None' currently breaks the code, since it will try to call 'None' as a function. Added the monomer checks to preserve compatibility.