public DateTimeStamp minus(double offsetInDecimalSeconds) {
        return add(-offsetInDecimalSeconds);
    }
@Test
    void testNanWithMinusNonZero() {
        assertThrows(IllegalArgumentException.class,
                () -> { new DateTimeStamp("2018-04-04T10:10:00.586-0100").minus(Double.NaN); },
                "IllegalAccess Not Thrown");
    }