Function is_empty_response 

fn is_empty_response(response: &mut Response, keys_answer: bool) -> bool

Whether a pass has nothing to answer the client with.

The key counts and fallback types are current state; they answer a pass the user’s watchers woke or one where the counts changed since pos. A woken answer lets matrix-rust-sdk back up its room keys. Both fields remain in the response whether or not they answer the pass.