Description

First step in fixing #914. cc @KnorpelSenf

Currently session has 2 "failure modes":

1. when getSessionKey(ctx) returns null, session remains unset
2. when there's no SessionData in store or it's expired, session is set to {}.

I believe changing the latter to also not set session would simplify things. The former behavior can be achieved with ctx.session ??= {} if desired.

I don't care about getting this merged; the typed way to attach (optional) data to ctx is WeakMap / https://yarnpkg.com/package/@emotion/weak-memoize.

How has this been tested?

This code continues passing typecheck:

import session from './session'
import Telegraf from './telegraf'
const bot = new Telegraf('')
bot.use(session())

session.ts itself has one type error that I cannot solve, hence draft.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes