The standard is to throw the NullPointerException. The generally infallible "Effective Java" discusses this briefly in Item 42 (first edition), Item 60 (second edition), or Item 72 (third edition) "Favor the use of standard exceptions":
"Arguably, all erroneous method
invocations boil down to an illegal
argument or illegal state, but other
exceptions are standardly used for
certain kinds of illegal arguments and
states. If a caller passes null in
some parameter for which null values
are prohibited, convention dictates
that NullPointerException be thrown
rather than IllegalArgumentException."
