protected function explode($commaSeparatedValues)
    {
        if (null === $commaSeparatedValues) {
            return array();
        }

        $array = explode(',', $commaSeparatedValues);

        if (array_walk(
            $array,
            function (&$item) {
            $item = strtoupper(trim($item));
            }
        )) {
            return $array;
        }

        return array();
    }