[Debug] Avoid notice from being "eaten" by fatal error.

Workaround for https://bugs.php.net/bug.php?id=54275. Follow-up to PR #9428 and #9449.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8703
| License       | MIT
| Doc PR        | n/a