code: private static synchronized PropertyDescriptor[] getPropertyDescriptors(final Class<?> clazz) {
          PropertyDescriptor[] descriptors = introspected.get(clazz);
          if (descriptors == null) {
              descriptors = getPDs(clazz);
              introspected.put(clazz, descriptors);
          }
          return descriptors;
      }
docs: Extract all {@link PropertyDescriptor}s for properties with getters and setters for the given
  class.
  
  @param clazz The class to extract the desired {@link PropertyDescriptor}s from
  @return All {@link PropertyDescriptor} for properties with getters and setters for the given
  class.