[orshih6]

When a respondent types into an optional short-text question that has a validation type (email, phone, number or regex) and then clears it, the frontend still sends [''] for that question. validateSubmission then passed the empty string to validateShortQuestion, which rejected it. The result was "Invalid input for question ..." and the form couldn't be submitted.

Empty answers are already dropped when answers are stored (storeAnswersForQuestion skips ''), so an empty short answer just means "not answered". Format validation is now skipped for it. Required questions are unaffected, because the earlier required check still rejects an empty answer with "Question ... is required.".

Tests: I added two testValidateSubmission data sets, an empty email answer on an optional question (now accepted) and on a required question (still rejected as required). The first one fails without this change. I ran the testValidateSubmission cases from SubmissionServiceTest with PHPUnit 10.5 and the nextcloud/ocp stubs, not a full server checkout, and they all pass. php-cs-fixer reports no changes.

Fixes #3802

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This change was prepared with an AI coding agent (Claude) and reviewed by me before submitting. I'm happy to make any changes you'd like.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Chartman123]

@orshih6 thanks for your contribution :) Please correctly sign-off your commit so that the pipeline gets green

[Chartman123]

/backport to stable5.4