See attached example
ZUL define tree -> controller attaches AbstractTreeModel to Tree. A dynamic tree is built where each root element always has 4 leaves.

• After scrolling the tree a root node is selected to expand = works the first time, the next selected root to expand runs into a NULL error in isLeaf as passed node == NULL.
• Select multiple root nodes without scrolling all functions according to expectations for the first selected node, scroll and next selection to expand will generate a NULL error in isLeaf.

How can a passed node become null? It seems something is loosing focus.