On PHP 8.6 putenv and getenv throw a ValueError when a name or value contains a null byte, and because the parser preserves null bytes and the repository name guard only rejects the empty string, such a byte reaches the putenv-backed adapter through a loaded file value or a direct set, get or clear call and crashes, uncaught, with safeLoad unable to suppress it. On earlier versions the same input is silently truncated at the null byte, which can quietly unset an unrelated variable. Guarding all three adapter methods against null bytes in the name, and the write against a null byte in the value, makes the operation simply fail, consistently across versions, matching the adapter's existing may-fail contract. This is stacked on #602 and is intended to land before v5.7.0 is tagged.