in a method i'm writing, i'd like to test for null elements in an
arbitrary set.
if the set contains a null element, i want to throw a NullPointerException.

rather than examining the elements myself, though i'd like to use the
Set.contains(Object) method.

here's the problem though:

in the java api it is possible for calling Set.contains(null) to throw a
NullPointerException if that set doesn't permit nulls in the first place.
(note, i doubt any implementation of Set actually does this, but i have to
follow the api.)

so, i can wrap my test in a try block:

try{
 if(myset.contains(null)) throw new NullPointerException("nulls not
 allowed...");
}
catch{NullPointerException e)
{
 // do something
}

the catch is needed to handle any Set objects that are passed that cannot
handle the contains(null) call.

but, i'd like to pass NullPointerException back up the call stack as is
done in the try block.

obviously though, if a null element is found, the catch block will catch
my NullPointerException that i want passed back up.

so, i have 2 solutions in mind:

1)  test each element one at a time manually using an iterator.

2)  create my own NullElementFoundException and handle it appropriately

but both of these solutions, while easy, are not particularly elegant.

anyone else ever have a situation like this with the java api and know of
a nice solution?

thanks