protected function exceptionIfNotString($key)
    {
        if (!is_string($key)) {
            throw new InvalidArgumentException(
                Message::get(Message::CONFIG_KEY_INVALID, $key),
                Message::CONFIG_KEY_INVALID
            );
        }
    }
protected function exceptionIfNotString($key)
    {
        if (!is_string($key)) {
            throw new InvalidArgumentException(
                Message::get(Message::CONFIG_KEY_INVALID, $key),
                Message::CONFIG_KEY_INVALID
            );
        }
    }
protected function exceptionIfNotString ( $ key ) { if ( ! is_string ( $ key ) ) { throw new InvalidArgumentException ( Message :: get ( Message :: CONFIG_KEY_INVALID , $ key ) , Message :: CONFIG_KEY_INVALID ) ; } }
Throw exception if not a string

@param  string $key
@throws InvalidArgumentException if $key not a string
@access public
Throw exception if not a string