Several public session history methods currently mistakenly return Option<T> because replaying a SEL with no events is valid, leaving the session in an Uninitialized state. PR #1014 removes the Uninitialized variant and enforces that every SEL must contain at least one event. After we remove the Unintialized state, we can remove the optional return type of session history methods that read from the first event. e.g fallback_tx and pj_param for the sender and session_context() & pj_uri() for the receiver.