4468566 added much better drop support to Swing components. While building demos for the JavaOne conference, I discovered a severe limitation with DropMode.INSERT in JTrees. If a folder node has no children, or is collapsed, it is impossible to insert an item into it.

In addition, I found a couple other small issues that should be addressed:

- We should support null for the "dropLineColor" and "dropLineShortColor" properties so that developers can use the UIManager to turn off the drop line indication.

- There is a minor bug with painting the drop line at the end of JTrees.