Possible bug: Parameter sweep pre-processing

[BenSchZA]

I have a query about cadCAD version 0.4.23 and parameter sweeps.

As far as I can remember the default behaviour of cadCAD is to pre-process the parameters, and extend all parameter lists to match the length of the longest parameter list, for example:

params = {
 'a': [1, 2, 3],
 'b': [0]
}

which is processed and becomes the following, for the last subset:

params = {
 'a': 3
 'b': 0
}

Instead, what currently happens is that the parameter 'b' isn't passed to the policy/state update functions, only for the last subset. If the behaviour has changed, that's okay, but I believe the default behaviour was to extend the parameter lists using the last entry as the default - this worked well.

[BenSchZA]

Here's a basic example of the issue: https://gist.github.com/BenSchZA/be5403e937c94c05f82cdcb905579b8e

[BenSchZA]

It seems that behaviour is only when there is a single parameter in the list, which makes sense.