Syntax fixes (#5367)

* Declare return types on functions

And a very few other type related minor fixes

* Minor syntax fixes

* Remove unnecessary escape chars in regexes
* Remove unnecessary awaits
* Replace deprecated req.connection with req.socket
* Replace deprecated upload with uploadOne
* Remove unnecessary eslint-disable-next-line comments
* Comment empty functions / catch or finally clauses
* Fix irregular whitespaces
* Add missing returns (null)
* Remove unreachable code
* A few logical fixes
* Remove / Handle non-null assertions which are certainly unnecessary (e.g. in
tests)

api/src/middleware/use-collection.ts

@@ -2,9 +2,10 @@
  * Set req.collection for use in other middleware. Used as an alternative on validate-collection for
  * system collections
  */
+import { RequestHandler } from 'express';
 import asyncHandler from '../utils/async-handler';
 
-const useCollection = (collection: string) =>
+const useCollection = (collection: string): RequestHandler =>
 	asyncHandler(async (req, res, next) => {
 		req.collection = collection;
 		next();