[ijl]

In [1]: bool(0)

Out[1]: False

Idiomatic Python may say "if not user_id:" and erroneously skip this.

[d0mine]

There is no `NULL` in Python. It is `None`.

Idiomatic test for `None` is:

   if something is None:
      # ...

It would be incorrect to use `if not something:` here.