One a TreeView with single item selection mode and one selected item, calling:

treeView.getSelectionModel().select(null)

causes:
- The selection event to get fired as old value = something, new value = null -
- the tree keeps highlighting the old selection
- treeView.getSlectionModel().getSelectedItem() returns null

I think either:
- the selection model doesn't accept null as it is not part of the tree model,
or
- the tree clears the selection

Is what one would expect