Fixes #294

[peterfarrell]

Fixes form validation crash for USZipCodeField when field is null=True, blank=True. See #294

Do not call strip on a None.

All Changes

• Add an entry to the docs/changelog.rst describing the change.

• Add an entry for your name in the docs/authors.rst file if it's not
  already there.

• Adjust your imports to a standard form by running this command:

  `isort --recursive --line-width 120 localflavor tests`
  

[codecov-io]

Codecov Report

Merging #295 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #295      +/-   ##
==========================================
+ Coverage   96.01%   96.01%   +<.01%     
==========================================
  Files         150      150              
  Lines        4165     4167       +2     
  Branches      566      567       +1     
==========================================
+ Hits         3999     4001       +2     
  Misses        107      107              
  Partials       59       59

Impacted Files	Coverage Δ
localflavor/us/forms.py	91.3% <100%> (+0.25%)	⬆️

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[benkonrath]

Thanks for the fix. Can you add a failing test that's fixed by this change? It should be enough to test the form field with empty_value set to None instead of the default empty string.
https://docs.djangoproject.com/en/1.11/ref/forms/fields/#charfield

[peterfarrell]

@benkonrath Added a test. It's a little hackish because Django < 1.11 don't support passing in empty_value to the field itself as it throws an unexpected argument error so instead of banging my head against the wall I went with the route that is in the test. Eventually it can be removed after support for Django < 1.11 happens.

Is there anything else you need to get this pulled in?

[benkonrath]

Seems like a good solution. I'll make a 1.5.1 release with this fix soon.