Invalid input for question "Email". #3802

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Describe the bug
This bug appears on forms containing a non-mandatory question requiring a specific format such as email or telephone (and probably others but I've only tested these two). If the user enters any text in the response field to the question requiring the specific format, then subsequently removes this text, leaving the field blank, an error occurs when the form is submitted and it is impossible to submit the form without completing this field with a valid value.

To Reproduce

1. Create a form with one optional short-text question, requiring an email address
2. Attempt to fill in this form : enter some text in the email field, then delete it, leaving the field empty
3. Press "Send"
4. Observe the error which complains of "Invalid input for question 'questionname'"

Expected behavior
The form should be submitted as if the question had been untouched

Nextcloud (please complete the following information):

• Nextcloud-Version: 35.0.2
• Forms-Version: 5.4.1

Additional Infomation
The error message appears in English, despite my nextcloud (and all other text on the page) being in French - I am aware this observation is not directly related to this bug but it would be great to get this fixed too :-)