Chained `previous_response_id` on `CreateResponseArgs` not correctly (imo) handling None values

[alexkunde]

Hi,

let's say i want to create a new request where my_prev_response_id is an Option, so i don't need to handle input myself.

let request = CreateResponseArgs::default().previous_response_id(my_prev_response_id).build()?;

From what i see in the documentation .previous_response_id() would normally handle Options, but seems to implement a bound requiring it to be a String.

#[serde(skip_serializing_if = "Option::is_none")]
    pub previous_response_id: Option<String>,

.previous_response_id(my_prev_response_id)
    |                  -------------------- ^^^^^^^^^^^^^^^^^^^^ the trait `From<std::option::Option<std::string::String>>` is not implemented for `std::string::String`
    |                  |
    |                  required by a bound introduced by this call

If implement logic to turn a None into an empty string, the API fails since the value must be filled with a valid id if provided.

2025-07-24T11:54:15.027613Z ERROR ai_server::handlers: Failed to get AI response: 
  Error creating response: 
  ApiError(ApiError { 
    message: "Invalid 'previous_response_id': ''. Expected an ID that contains letters, numbers, underscores, or dashes, but this value contained additional characters.", 
    type: Some("invalid_request_error"), 
    param: Some("previous_response_id"), 
    code: Some("invalid_value") })

Can you remove the bound so we can let serde handle the value and correctly remove it if its none?

Thank you for your consideration!