@Override
    public PersistableMap<String, String> loadProperties(Group group)
    {
        return getGroupProvider(group.getName()).loadProperties(group);
    }
Loads the group properties (if any) from the backend data store. If the properties can be changed, the provider
implementation must ensure that updates to the resulting {@link Map} are persisted to the backend data store.
Otherwise, if a mutator method is called, the implementation should throw an {@link UnsupportedOperationException}.

If there are no corresponding properties for the given group, or if the provider does not support group
properties, this method should return an empty Map rather than null.

@param group The target group
@return The properties for the given group
xmppserver/src/main/java/org/jivesoftware/openfire/group/GroupMultiProvider.java