Unknown password hashing algorithm error if password is blank

[Leo Shklovskii]

Related to #18182 - if the password on the user is blank, Django crashes with the error: Unknown password hashing algorithm ''. Did you specify it in the PASSWORD_HASHERS setting?

[Claude Paroz]

Could you please specify at which point does the crash occurs? I've worked on #18182, and I would like to be sure that your use case is addressed.

[Leo Shklovskii]

Sorry, to clarify, it hits the ValueError which results in a 500:

File "/foo/lib/python2.7/site-packages/django/contrib/auth/hashers.py", line 115, in get_hasher
  "setting?" % algorithm)

File "/foo/lib/python2.7/site-packages/django/contrib/auth/hashers.py", line 42, in check_password
  hasher = get_hasher(algorithm)

File "/foo/lib/python2.7/site-packages/django/contrib/auth/models.py", line 304, in check_password
  return check_password(raw_password, self.password, setter)

That happens because the algorithm ends up being ''

[Claude Paroz]

This should be fixed if current patch of #18182 is committed, however let this one open until then.

[Claude Paroz <claude@…>]

In 703c266682be39f7153498ad0d8031231f12ee79:

Fixed #18182 -- Made is_usable_password check if hashing algorithm is correct

The display of the ReadOnlyPasswordHashWidget has also been improved to
distinguish empty/unusable password from erroneous password.
Fixed #18453 also.
Thanks danielr and Leo for the reports and Moritz Sichert for the
initial patch.