Fix updating custom filed of type JSON

[Kani999]

Close #457

Since there is no existing PR, I've created one which is based on @markkuleinio solution

[FliesLikeABrick]

+1 I installed pynetbox from this branch and it resolved my inability to update JSON custom properties with the error cited in #457

[FliesLikeABrick]

@zachmoody can you review this? It would be great to have this fix come in upstream to fix our automation and let us avoid having to create an internal fork

[abhi1693]

@Kani999 This change does not seem to be the right way to handle this scenario. IMO, you should update the flatten_custom to something like

def flatten_custom(custom_dict):
    return {
        k: v if not isinstance(v, dict) else v["id"] for k, v in custom_dict.items()
    }

custom_dict always contains the id field which I believe used to be referred to as value in the older versions.

[Kani999]

@abhi1693 I've changed the flatten_custom method, which basically does nothing at the moment. So it works like a previous change.

custom_dict always contains the id field which I believe used to be referred to as value in the older versions.

That's not true. Item contains just a key and value, there is no id or anything else. Example of custom_dict parameter:

type(custom_dict) <class 'dict'>

{'TEST': 'blah blah blah', 
 'json_data': {'a': 1, 
               'b': 2}}

[rodvand]

Any news on merging this? The issue this PR addresses also affects the ansible modules.