public static function getCamelCase($string, $separator = ' ')
    {
        if (empty($string)) {
            return '';
        }

        $effect = '';
        $members = explode($separator, $string);

        foreach ($members as $key => $value) {
            $value = mb_strtolower($value);

            if (0 === $key) {
                $effect .= self::lowercaseFirst($value);
            } else {
                $effect .= self::uppercaseFirst($value);
            }
        }

        return $effect;
    }