public static function upperCase(?string $string = null): ?string
    {
        if ($string === null) {
            return null;
        }

        return mb_strtoupper($string, 'UTF-8');
    }
public static function upperCase(?string $string = null): ?string
    {
        if ($string === null) {
            return null;
        }

        return mb_strtoupper($string, 'UTF-8');
    }
public static function upperCase ( ? string $ string = null ) : ? string { if ( $ string === null ) { return null ; } return mb_strtoupper ( $ string , 'UTF-8' ) ; }
Change content to upper case. Analog of strtoupper with UTF-8
@param string|null $string
@return string|null
Change content to upper case . Analog of strtoupper with UTF - 8