These comments were pulled from the comments section of bug 4655513 describing another bug unrelated to that original bug. See the attached code to demonstrate the problem.

  This is something else which is not related to above
  problem, but you can see this error when you drag
  something from MyTree over to the MyTable but not
  drop it, and then take the dragged data out of the
  component. You will see a NullPointerException
  generated at BasicTableUI.java:1216.

It is not known yet whether this bug occurs on platforms other that windows.