@SuppressWarnings("deprecation")
    public void testFactoryFieldDifference2() throws Throwable {
        YearMonthDay ymd = new YearMonthDay(2005, 4, 9);
        try {
            Period.fieldDifference(ymd, (ReadablePartial) null);
            fail();
        } catch (IllegalArgumentException ex) {}
        try {
            Period.fieldDifference((ReadablePartial) null, ymd);
            fail();
        } catch (IllegalArgumentException ex) {}
    }