Model attributes need to be JSON serializable

[PeterLombaers]

Describe the bug
When you create a model extension class an attribute which is an argument to class.__init__ and which is not json serializable, the state class will complain when saving the settings.

To Reproduce
Create a model extension with an attribute that is not json serializable and run a simulation.

Additional context
The state class stores the settings and metadata as a json (see here). Part of the settings object is the parameters of the different model parts. These parameters are set here. This param property of BaseModel is constructed by looping over parameters in the signature of class.__init__ and getting the current values of these parametes as a class attribute. If the current value is not json serializable, this will give a problem when the state class tries to store the settings.

Another problem is that this method of storing the model parameters only works if the arguments to __init__ are actually used as class attributes, which need not be the case.

[PeterLombaers]

One quick fix on the side of the model extension is to override the param property to return something that is json serializable.

[J535D165]

Good catch.

One quick fix on the side of the model extension is to override the param property to return something that is json serializable.

Alternative quick fix: What about providing the class json serializable arguments? Convert them to the desired structure internally (e.g fit method).