code: public static Class<?> getPrimitiveClass(final Class<?> clazz) {
  
      if (clazz == null) {
        return null;
      }
      int index = ArrayUtils.indexOf(WRAPPER_CLASSES, clazz);
      if (index != ArrayUtils.INDEX_OF_NOT_FOUND) {
        return PRIMITIVE_CLASSES[index];
      }
      return clazz;
    }
docs: Returns given class primitive class or self class.<br>
  if given class is 8 wrapper class then return primitive class.<br>
  if given class is null return null.
  
  @param clazz class to handle.
  @return given class primitive class or self class.