in src/ExpectObj.hack [486:494]
public function toNotContainKey<TKey as arraykey, TVal>(
TKey $key,
string $msg = '',
mixed ...$args
): void where T as KeyedContainer<TKey, TVal> {
$msg = \vsprintf($msg, $args);
$obj = $this->var;
$this->assertFalse(\array_key_exists($key, $obj), $msg);
}