code: public Set<ElementDescriptor<?>> getPropertyDescriptors()
  	{
  		return mProperties == null ? null : Collections.unmodifiableSet(mProperties.keySet());
  	}
docs: Returns the {@link Set} of properties in this PropStat element, each represented by its {@link ElementDescriptor}s.
  
  @return A {@link Set} of {@link ElementDescriptor}s or <code>null</code>.