Is this behavior properly documented? If not, it's a bug.
public void testAddNull() {
Fraction a = Fraction.getFraction(5, 3);
try {
Fraction f = null;
a.add(null);
fail("added null");
}
catch (IllegalArgumentException success) {
// This really is a bug. This should be a NullPointerException
assertNotNull(success.getMessage());
}
}