feat: add support for null args on create_and_run

[pietroMonta42]

Input:

client.beta.threads.create_and_run(
                assistant_id= "'asst_WoQW7v5aOWGk7118yPUgqQcj'",
                thread={
                    "messages": [
                        {"role": "user", "content":"Hi"}
             ]
                },
                model=None,
                instructions=None,
                tools=None
            )

Error:

respx.models.SideEffectError: <Route <Scheme eq 'https'> AND <Host eq 'api.openai.com'> AND <Method eq 'POST'> AND <URL regex re.compile('/v1/threads/runs')>>

The above exception was the direct cause of the following exception:

pydantic_core._pydantic_core.ValidationError: 3 validation errors for Run
instructions
  Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.7/v/string_type
model
  Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.7/v/string_type
tools
  Input should be a valid list [type=list_type, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.7/v/list_type

The above exception was the direct cause of the following exception:
    run = self.client.beta.threads.create_and_run(

I have seen that on the official API None parameters are allowed

[mharrisb1]

Thanks for reporting @pietroMonta42

The problem seems straightforward so I'll push out a fix as soon as I can