raise SubstitutionError("Unknown variable or function '%s' while performing substitution on '%s'" % (v, c))
if r is None:
raise SubstitutionError("Substitution for '%s' is null while performing substitution on '%s'" % (v, c))
raise SubstitutionError("Unknown variable or function '%s' while performing substitution on '%s'" % (v, c))
if r is None:
raise SubstitutionError("Substitution for '%s' is null while performing substitution on '%s'" % (v, c))