public void testSet_Field() {
        MutablePeriod test = new MutablePeriod(1, 2, 3, 4, 5, 6, 7, 8);
        test.set(DurationFieldType.years(), 10);
        assertEquals(10, test.getYears());
        
        test = new MutablePeriod(1, 2, 3, 4, 5, 6, 7, 8);
        try {
            test.set(null, 10);
            fail();
        } catch (IllegalArgumentException ex) {}
    }