AddressNL unreliable validation fix

[robinmolen]

Make sure that get emptyValue() stays a regular function. Making the get emptyValue() static results into weird validation issues, broken e2e tests, and general unpleasant behavior.

[codecov]

Bundle Report

Changes will increase total bundle size by 176 bytes (0.0%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
@open-formulieren/sdk-OpenForms-umd	4.77MB	88 bytes (0.0%) ⬆️
@open-formulieren/sdk-esm	4.75MB	88 bytes (0.0%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: @open-formulieren/sdk-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/formio-*.js	88 bytes	2.03MB	0.0%

Files in assets/formio-*.js:

• ./src/formio/components/AddressNL.jsx → Total Size: 13.71kB

view changes for bundle: @open-formulieren/sdk-OpenForms-umd

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
open-*.js	88 bytes	3.49MB	0.0%

Files in open-*.js:

• ./src/formio/components/AddressNL.jsx → Total Size: 13.73kB

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.67%. Comparing base (263df05) to head (e70a702).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #790      +/-   ##
==========================================
+ Coverage   83.65%   83.67%   +0.02%     
==========================================
  Files         244      244              
  Lines        4777     4777              
  Branches     1268     1268              
==========================================
+ Hits         3996     3997       +1     
+ Misses        748      747       -1     
  Partials       33       33              

Flag	Coverage Δ
storybook	76.25% <100.00%> (ø)
vitest	63.00% <0.00%> (+0.04%)	⬆️

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