public final void drainerFailed(Throwable t) {
        if (t == null) {
            throw new NullPointerException("ConcurrentConveyor.drainerFailed(null)");
        }
        drainer = null;
        drainerDepartureCause = t;
    }
@Test(expected = NullPointerException.class)
    public void when_callDrainerFailedWithNull_then_throwNPE() {
        conveyor.drainerFailed(null);
    }