NULL != 0.

That never stopped JavaScript, Python and friends from giving them equal truthiness.

Ehm, Python doesn't have a NULL:

  >>> NULL == 0
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  NameError: name 'NULL' is not defined

Even None, which is as close to NULL you are going to get in Python is not 0.

  >>> None == 0
  False

This is probably what the parent meant:

    >>> 'truthy' if None else 'falsy'
    'falsy'
    >>> 'truthy' if False  else 'falsy'
    'falsy'
    >>> 'truthy' if 0 else 'falsy'
    'falsy'

> That never stopped JavaScript, Python and friends from giving them equal truthiness.

Implicit casts -- including to booleans -- are dangerous, but if you try to write APIs to try to avoid every bad thing that might happen with naive use of implicit casting in every language that might be used to consume your API, you won't be able to do anything at all.

"truthiness" is true/false and NOT NULL! 0 != null null != false

In [1]: bool(0)

Out[1]: False

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

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.