code: public static function UPPERCASE($mixedCaseString)
      {
          $mixedCaseString = Functions::flattenSingleValue($mixedCaseString);
  
          if (is_bool($mixedCaseString)) {
              $mixedCaseString = ($mixedCaseString) ? Calculation::getTRUE() : Calculation::getFALSE();
          }
  
          return StringHelper::strToUpper($mixedCaseString);
      }
docs: UPPERCASE.
  
  Converts a string value to upper case.
  
  @param string $mixedCaseString
  
  @return string