protected function connect(
        $username,
        $password,
        $connectionString = null,
        $characterSet = null,
        $sessionMode = null
    ) {
        set_error_handler(static::getErrorHandler());
        $connection = oci_new_connect($username, $password, $connectionString, $characterSet, $sessionMode);
        restore_error_handler();
        return $connection;
    }