Method hasKey

/**
 * Determines is a key exists.
 *
 * @param   string  $string  The key to check.
 *
 * @return  boolean  True, if the key exists.
 *
 * @since   1.7.0
 */
public function hasKey($string)
{
    if ($string === null) {
        return false;
    }
    return isset($this->strings[strtoupper($string)]);
}