A NullPointerException occurs when the stylesheet is
supplied as a DOMSource with no systemId, or when the
source document is supplied this way and the standard
tree model is used.
(This is another occurrence of a long-running problem;
it's proving very difficult to track down all the
paths that are dependent on a system ID being
Raised by Dane Foster [email@example.com]
Present in 6.4.3 and in previous releases (although
masked in previous releases by other errors).
Source code has been fixed and tested.
Circumvention: call setSystemId() on the Source
object, supplying an empty string as the systemId.