Making the input parameter optional in responses

API
1

I would like to create a response from a conversation without giving additional input, however the API throws an error that input is a required parameter. Why is this, if my conversation contains the user message that I would like to see a response to? Could input be made optional?

Intended use:

conversation = client.conversations.create(
    items=[
        {
            "role": "user",
            "content": "Just a simple test."
        }
    ]
)

response = client.responses.create(
    model="gpt-4.1",#"gpt-5.6-luna",
    store=True,
    background=True,
    conversation=conversation.id,
)