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

Workaround for https://bugs.php.net/bug.php?id=54275.

    | 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