Flask cli user show should return message when user doesn't exist

flask cli user show <non-existing-user> returns a stack trace instead of a readable message:

❯ stack user show admin
None

Traceback (most recent call last):
  File "/usr/local/bin/flask", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.10/site-packages/flask/cli.py", line 995, in main
    cli.main(args=sys.argv[1:])
  File "/usr/local/lib/python3.10/site-packages/flask/cli.py", line 601, in main
    return super().main(*args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1053, in main
^[[A    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1659, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1659, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1395, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.10/site-packages/click/core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/click/decorators.py", line 26, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/flask/cli.py", line 445, in decorator
    return __ctx.invoke(f, *args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/click/core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "/usr/src/app/app.py", line 217, in show_user
    print(f"UUID:     {user.uuid}")
AttributeError: 'NoneType' object has no attribute 'uuid'
command terminated with exit code 1