Bugfix/swi 63 handle empty policy area

[Tschuppi81]

SWI: Ignore empty policy area

TYPE: Bugfix LINK: swi-63

Checklist

• [x] I have performed a self-review of my code
• [x] I considered adding a reviewer
• [x] I have tested my code thoroughly by hand
• [x] I have added tests for my changes/features

[Tschuppi81]

Is there a way to influence the converters to handle this case?

[codecov[bot]]

Codecov Report

:x: Patch coverage is 95.23810% with 2 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 86.41%. Comparing base (444995f) to head (ddc3461). :warning: Report is 164 commits behind head on master. :white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/onegov/core/filters.py	81.81%	2 Missing :warning:

Additional details and impacted files

Files with missing lines	Coverage Δ
src/onegov/swissvotes/collections/votes.py	98.92% <100.00%> (+<0.01%)	:arrow_up:
src/onegov/swissvotes/converters.py	100.00% <100.00%> (ø)
src/onegov/swissvotes/path.py	97.82% <100.00%> (+0.04%)	:arrow_up:
src/onegov/core/filters.py	86.95% <81.81%> (-3.96%)	:arrow_down:

... and 2 files with indirect coverage changes

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[Daverball]

Is there a way to influence the converters to handle this case?

Yes, you can write a custom converter for the policy area format, so any values that don't conform to the format get dropped.

Ideally we change the collection to accept list[PolicyArea] instead and write a converter for PolicyArea that verifies the format, split the string over . and make sure each component is numeric and starts with the previous component.