code: @Override
  	public void registerPropertyGroup(Class type, PropertyKey key, PropertyGroup propertyGroup) {
  		getPropertyGroupMapForType(type).put(key.dbName(), propertyGroup);
  	}
docs: Registers a property group for the given key of the given entity
  type. A property group can be used to combine a set of properties
  into an object.
  
  @param type the type of the entities for which the property group
  should be registered
  @param key the property key under which the property group should be
  visible
  @param propertyGroup the property group