@Override
    protected Mono<Void> getFallback() {
        if (isFailedExecution()) {
            LOG.error("hystrix execute have error: ", getExecutionException());
        }
        final Throwable exception = getExecutionException();
        return fallback(exchange, getCallBackUri(), exception);
    }
@Test
    public void testGetFallback() {
        assertThrows(NullPointerException.class, () -> StepVerifier.create(hystrixCommandOnThread.getFallback()).expectSubscription().verifyComplete());
    }