The last assertNull in IterableUtilsTest.find is redundant

The last assertNull in IterableUtilsTest.find (line 277, as shown
below), is redundant and confusing; it will not be invoked because
IterableUtils.find(*, null) should not return any value but just throw
NullPointerException. I will make a PR to clarify this.

try {
    assertNull(IterableUtils.find(iterableA, null));
    fail("expecting NullPointerException");
} catch (final NullPointerException npe) {
    // expected
}