Update Fehler auf 5.2.20 (1048 Column 'form_id' cannot be null)

Sämtliche Updates verliefen bisher problemlos, doch jetzt..

Wie kann dieses Problem gelöst werden?

Error
Received the following error message:
Could not apply migration (Migrations_Migration815). Error: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'form_id' cannot be null

Please try to fix this error and restart the update.
Response

{"valid":false,"errorMsg":"Could not apply migration (Migrations_Migration815). Error: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'form_id' cannot be null "}