The example is an implemenation of TreeItem wrapping the file system. The initial leaf-ness of directories is inconsistent for getter vs. property, failing test snippet:

        TreeView<File> tree = buildFileSystemBrowser();
        for (TreeItem child : tree.getRoot().getChildren()) {
            assertEquals(child.isLeaf(), child.leafProperty().get());
        }

The reason is that sub-classes can't access leafProperty (already reported in RT-37386 and others), so I see no way to initialize the property correctly (short of going dirty and expand the node temporarily or reflective access).

This is meant as a reminder to update the example once the reason is fixed.