fix: fall back to default value if foreign key of join_numpy is unresolved

[lars-reimann]

What problem do you want to solve?

Closes #740

join_numpy now takes a value that is used if a foreign key cannot be resolved, e.g. because it is explicitly set to -1.

Todo

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[lars-reimann]

1. Currently, a default value must always be specified. Would that suffice for now?
2. Should there still be a check of the validity of foreign keys? I've kept it for non-negative foreign keys.
3. A default value for _unterhaltsvorschuss_empf_eink_above_income_threshold must still be added.

[hmgaudecker]

1. I think the name "default" is misleading a bit. Maybe: "value_if_foreign_key_is_missing"? Too long, maybe... But yes, we should be explicit there.
2. Validity checks for non-negative numbers sound good.
3. That'll be up to @MImmesberger

Thanks!!!

[MImmesberger]

Thanks, that was fast!
I tried it out on the branch of #739 and it works as expected. Regarding the naming: I think value_if_foreign_key_is_missing makes it clearer what is happening for the average user than value_for_unresolved_foreign_key.

[MImmesberger]

I just renamed the new argument and adjusted the join for Unterhaltsvorschuss accordingly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.41%. Comparing base (23e7b4f) to head (42c5eca).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #741   +/-   ##
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  Coverage   89.41%   89.41%           
=======================================
  Files          51       51           
  Lines        3646     3647    +1     
=======================================
+ Hits         3260     3261    +1     
  Misses        386      386           

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[hmgaudecker]

Great, thanks! Approval conditional on fixed tests, ofc. (feel free to merge if they'll be fixed immediately in another PR).