The widget form code for "Validate closed paragraphs and expand if needed." checks all fields on the paragraph and does not limit validation to the fields in the form display.
When the paragraphs widget validates a "closing" form, then it does not highlight any field and shows errors messages that are confusing to editors "This value should not be null.".
Proposed:
1. Allow the widget elementValidate() to flag the errors on the widget forms as it normally would. This provides human understandable error messages and highlights the field.
FIX to implement: Update collapse_button to limit validation to the field item.
2. Keep on form build validation for "" in case there is some edge case that is it still needed.
FIX to implement: Update code to check for a field widget similar to EntityFormDisplay::flagWidgetsErrorsFromViolations().
1.0
Code
The change is currently missing an automated test that fails when run with the original code, and succeeds when the bug has been fixed.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Patch #55 works on paragraphs 8.x-1.15.0 and Drupal 9.4.4.
The error message is gone:
Validation error on collapsed paragraph field_view: This value should not be null.
Unfortunately, module " save_edit → " version 8.x-1.4 does not work anymore with it.