ErrorException on 400 Responses without Violations

[Rainrider]

When an API returns a 400 response without validation violations, AbstractConstraintViolationListDenormalizer throws an ErrorException 'Warning: Undefined array key "violations"'

400: Bad Request responses in Api Platform normally do not have details on validation violations (those are normally contained in 422: Unprocessable Entity). An example for such response is when an IRI cannot be resolved to a resource which is then resolved to a 400 status code.