Fix processing additionalProperties when bool-type

[Matthijsy]

I am just starting to use rigging, in combination with the fabric-rti-mcp. Using this crashed the _process_field since it returns a schema like this:

{'additionalProperties': True, 'type': 'object'}

This results in trying to process True as a dict. This PR first checks if the additionalProperties value actually is a dict before processing.

Please let me know if there is any feedback.

[l50]

Thanks for catching this bug and providing the fix! The isinstance(additional_schema, dict) check definitely prevents the crash.

One thing to consider: according to JSON Schema spec, additionalProperties: true means "allow any additional properties of any type," which should map to dict[str, Any] in Python.

Your current fix prevents the crash but causes additionalProperties: true to fall through to the nested model case, which might not be the intended behavior.

Here's a more complete fix:

if additional_schema:
    if additional_schema is True:
        return dict[str, t.Any], field_info
    elif isinstance(additional_schema, dict):
        dict_type, _ = _process_field(f"{field_name}Item", additional_schema)
        return dict[str, dict_type], field_info

This way:

• additionalProperties: {schema} → typed dict (your original case)
• additionalProperties: true → dict[str, Any] (fabric-rti-mcp case)
• additionalProperties: false or missing → nested model