Handle special rate laws better

mira/metamodel/template_model.py

@@ -302,14 +302,16 @@ def get_parameters_from_rate_law(self, rate_law) -> Set[str]:
  :
  A set of parameter names (as strings)
  """
- if not rate_law:
+ if rate_law is None:
  return set()
  params = set()
  if isinstance(rate_law, sympy.Symbol):
  if rate_law.name in self.parameters:
  # add the string name to the set
  params.add(rate_law.name)
- elif not isinstance(rate_law, sympy.Expr):
+ # There are many sympy classes that have args that can occur here
+ # so it's better to check for the presence of args
+ elif not hasattr(rate_law, 'args'):
  raise ValueError(f"Rate law is of invalid type {type(rate_law)}: {rate_law}")
  else:
  for arg in rate_law.args: