Serialize template rate laws to be None if the rate law doesn't exist

mira/metamodel/templates.py

@@ -458,7 +458,7 @@ def from_json(cls, data, rate_symbols=None) -> "Template":
 
  @field_serializer('rate_law')
  def serialize_expression(self, rate_law):
- return str(rate_law)
+ return str(rate_law) if rate_law is not None else None
 
  def is_equal_to(self, other: "Template", with_context: bool = False,
  config: Config = None) -> bool:

tests/test_model_api.py

@@ -589,18 +589,19 @@ def test_n_way_comparison_askenet(self):
  "exclude_defaults": True,
  "exclude_unset": True,
  "exclude_none": True,
- # This key is outdated in Pydantic2
- # "skip_defaults": True,
  }
  # Compare the ModelComparisonResponse models
  # If assertion fails the diff is printed
+ # Use model dump as Pydantic objects have an attribute
+ # "model_fields_set" that contain explicitly set attributes even if
+ # are None
  assert local_response.model_dump() == resp_model.model_dump()
  local_sorted_str = sorted_json_str(
- json.loads(local_response.model_dump_json()),
+ json.loads(local_response.model_dump_json(**dict_options)),
  skip_empty=True
  )
  resp_sorted_str = sorted_json_str(
- json.loads(resp_model.model_dump_json()),
+ json.loads(resp_model.model_dump_json(**dict_options)),
  skip_empty=True
  )
  self.assertEqual(local_sorted_str, resp_sorted_str)