- run the attached code
- click to expand the root node
- observe the "expand" triangle icon at the bottom of the window (problem 1)
- press Change Root button
- make the window height larger
- notice the second artifact

The issue seems to be caused by setting a root TreeItem with either a null value
`new TreeItem<>(null)`
or the null wrapped value
`new TreeItem<>(new Entry(null))`

starting on line 43

Using a non-null value works fine ``new TreeItem(new Entry("Root"))`

This might be related to a similar issue in TreeTableView. JDK-8341281