public static <U extends Enum<U> & PhysicalUnit> void assertNonNegativeOrNull(Quantity<U> quantity) {
		if(quantity != null)
			quantity.assertNonNegative();
	}
@Test()
    public void nullQuantity_passesOnCheckForNonNegative() throws Exception {
        Quantity.assertNonNegativeOrNull(null);
    }