code: @Override
  	public final Enumeration<String> getPropertyNames()
      {
      	assertDeserializationLevel(MessageSerializationLevel.ALL_HEADERS);
      	
      	if (propertyMap == null)
      		return new EmptyEnumeration<>();
      		
          return new IteratorEnumeration<>(propertyMap.keySet().iterator());
      }
docs: /*
  (non-Javadoc)
  @see javax.jms.Message#getPropertyNames()