Backend throws unhandled exception when non-existent user communicates

[ghost]

Reproduce:

• Start backend
• Start frontend
• Log into page
• Stop Backend
• Start backend (with "eraseOnStartup": true) so the user-IDs are different now
• Return to website and click something that starts a http-request to the backend
• Backend throws unhandled exception

(node:908) UnhandledPromiseRejectionWarning: Error: Error: User does not longer exist in database!
    at D:\DEV\GIT\github\DocSort\backend\src\lib\jwt.ts:33:15
    at step (D:\DEV\GIT\github\DocSort\backend\src\lib\jwt.ts:32:23)
    at Object.next (D:\DEV\GIT\github\DocSort\backend\src\lib\jwt.ts:13:53)
    at fulfilled (D:\DEV\GIT\github\DocSort\backend\src\lib\jwt.ts:4:58)
    at processTicksAndRejections (internal/process/next_tick.js:81:5)
(node:908) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:908) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not
handled will terminate the Node.js process with a non-zero exit code.