[8.x] Pass null to custom cast set method when value is null

[jnoordsij]

When using a custom cast class for casting attributes on a model, it is currently impossible to add custom behavior when the value set equals to null. This is due to the fact that in this case there is a manual catch that calls the setter with the current model value instead of the given null value.

By the looks of it, I think the purpose of this clause is to automatically set all attributes values provided by the class set method equal to null, which sounds reasonable but then again prevents users for adding custom behavior. It might be even better to remove the clause altogether (though this probably should be considered a breaking change), any feedback is appreciated!

[taylorotwell]

I don't think we can change any behavior related to this on a patch release?

[jnoordsij]

This change actually doesn't change the behavior really; the only thing that changes is the set call receiving null (as one would expect when setting a property to null) instead of "old value". The array_map callback still results in all attribute values being forcibly changed to null, regardless of the output of the cast.

Maybe this doesn't really help all that much, especially considering no one else has stumbled upon this problem yet, so it might be better if I create a PR targetting master that removes the clause altogether to allow users to have custom logic for handling null values.

[GrahamCampbell]

The fact that no tests broke means there is not sufficient test coverage here. Can you add a new test that used to fail, but after your changes, now passes?

[taylorotwell]

Agree with @GrahamCampbell's comment. That would be helpful.

[taylorotwell]

Marking as draft for now - please mark as active once that has been done.

[jnoordsij]

I added a test based on the example in the docs.

[taylorotwell]

I really don't think I can merge this on a patch on further thought. I'll think about it for the 9.x release.