public void testGetPeriodConverterRemovedNull() {
        try {
            ConverterManager.getInstance().removePeriodConverter(NullConverter.INSTANCE);
            try {
                ConverterManager.getInstance().getPeriodConverter(null);
                fail();
            } catch (IllegalArgumentException ex) {}
        } finally {
            ConverterManager.getInstance().addPeriodConverter(NullConverter.INSTANCE);
        }
        assertEquals(PERIOD_SIZE, ConverterManager.getInstance().getPeriodConverters().length);
    }