public DateTimeStamp minus(double offsetInDecimalSeconds) {
        return add(-offsetInDecimalSeconds);
    }
@Test
    void testNanWithMinus() {
        DateTimeStamp dateTimeStamp = new DateTimeStamp("2018-04-04T10:09:59.586-0100");
        DateTimeStamp forComparing = new DateTimeStamp("2018-04-04T10:10:00.586-0100").minus(1.0d);
        assertEquals(dateTimeStamp, forComparing);
    }