fix(binding): improve empty slice/array handling in form binding

[1911860538]

This ensures that empty slices/arrays properly use default values when available,
and prevents index out of bounds errors when no defaults exist.
Fixes #4377

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.92%. Comparing base (3dc1cd6) to head (71dee21).
⚠️ Report is 191 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4380      +/-   ##
==========================================
- Coverage   99.21%   98.92%   -0.29%     
==========================================
  Files          42       44       +2     
  Lines        3182     3446     +264     
==========================================
+ Hits         3157     3409     +252     
- Misses         17       26       +9     
- Partials        8       11       +3     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	98.91% <100.00%> (?)
-tags go_json	98.86% <100.00%> (?)
-tags nomsgpack	98.91% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.23	98.92% <100.00%> (?)
go-1.24	98.92% <100.00%> (?)
go-1.25	98.92% <100.00%> (?)
macos-latest	98.92% <100.00%> (-0.29%)	⬇️
ubuntu-latest	98.92% <100.00%> (-0.29%)	⬇️

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[Copilot]

Pull Request Overview

This PR fixes empty slice/array handling in form binding to properly use default values when available and prevents index out of bounds errors when no defaults exist. It addresses issue #4377.

Key changes:

• Modified the condition from checking form field presence to checking if the field has empty values
• Added proper handling for cases where no default value exists for empty slices/arrays
• Ensured default values are applied when empty arrays/slices are encountered

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
binding/form_mapping.go	Updated slice and array handling logic to check for empty values instead of field presence
binding/form_mapping_test.go	Added comprehensive test coverage for empty slice/array scenarios with and without defaults

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[Copilot]

The condition len(vs) == 0 will be true both when the field is not present in the form (ok == false) and when the field is present but has an empty slice. Consider adding a comment to clarify this intentional behavior change from the previous !ok check.

[Copilot]

The condition len(vs) == 0 will be true both when the field is not present in the form (ok == false) and when the field is present but has an empty slice. Consider adding a comment to clarify this intentional behavior change from the previous !ok check.