RichFaces: "UITree.getModelTreeNode" function does not exist in RF 4.x any more

I'm trying to migrate an application from RF 3.3.7 to RF 4.X.

Issue: The following command does not exist any more:

getModelTreeNode(java.lang.Object rowKey) 

Has anyone any idea how to work around or an alternative approach with the same result? I googled for hours now :/

Thanks in advance!