The format string "%ld" is used in a couple of places but not supported:

http://download.oracle.com/javase/6/docs/api/java/util/Formatter.html#syntax

This may cause an exception to be thrown while throwing an exception.

Also, it is not necessary to test for a negative-valued native handle: we have no idea whether the value will be negative as it is a native pointer formatted to a Java long. The only known invalid value is zero.