public static SessionWindows ofInactivityGapWithNoGrace(final Duration inactivityGap) {
        return ofInactivityGapAndGrace(inactivityGap, ofMillis(NO_GRACE_PERIOD));
    }
@Test
    public void windowSizeMustNotBeNegative() {
        assertThrows(IllegalArgumentException.class, () -> SessionWindows.ofInactivityGapWithNoGrace(ofMillis(-1)));
    }