`Locale.parse()` no longer accepts None as the locale identifier

[neuroid]

Overview Description

Locale.parse() no longer accepts None as the locale identifier, contrary to the type annotation.

Steps to Reproduce

>>> from babel import Locale
>>> Locale.parse(None) is None

Actual Results

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/env/lib/python3.8/site-packages/babel/core.py", line 317, in parse
    raise TypeError(f"Unexpected value for identifier: {identifier!r}")
TypeError: Unexpected value for identifier: None

Expected Results

True

Reproducibility

👍

Additional Information

Arguably, the previous behaviour was useful. However, if this breaking change is intentional, the type annotation should be adjusted accordingly.

[akx]

This change was intentional (happened in #966) (but I forgot to distil it into the changelog).

Why would the behaviour be useful?