public void testGetDurationConverterRemovedNull() {
        try {
            ConverterManager.getInstance().removeDurationConverter(NullConverter.INSTANCE);
            try {
                ConverterManager.getInstance().getDurationConverter(null);
                fail();
            } catch (IllegalArgumentException ex) {}
        } finally {
            ConverterManager.getInstance().addDurationConverter(NullConverter.INSTANCE);
        }
        assertEquals(DURATION_SIZE, ConverterManager.getInstance().getDurationConverters().length);
    }