public function has(string $key = null) : bool
    {
        if ($key === null) {
            return false;
        }

        return $this->offsetExists($key);
    }
public function has(string $key = null) : bool
    {
        if ($key === null) {
            return false;
        }

        return $this->offsetExists($key);
    }
public function has ( string $ key = null ) : bool { if ( $ key === null ) { return false ; } return $ this -> offsetExists ( $ key ) ; }
Check for existence.

@param string $key

@return bool
Check for existence .