No notice is thrown for list() accesses, because we did not come
to an agreement regarding patterns like
while ([$key, $value] = yield $it->next()) { ... }
where silent null access may be desirable.
No effort is made to suppress multiple notices in access chains
likes $x[0][0][0], because the technical complexity this causes
does not seem worthwhile.
RFC: https://wiki.php.net/rfc/notice-for-non-valid-array-container
