- [ ] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [ ] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Steps to reproduce this issue

1. 提交PR，Travis CI build failed，原因为单元测试不通过
![image](https://user-images.githubusercontent.com/33019873/80856713-bcd40180-8c7e-11ea-8a26-d50021587e85.png)
2. 单元测试要求直接报异常
![image](https://user-images.githubusercontent.com/33019873/80856717-d412ef00-8c7e-11ea-88a3-620b86ddecbe.png)
3. 5月1号解决[#5916]时，将默认方法修改了，现在不会报异常出来
![image](https://user-images.githubusercontent.com/33019873/80856741-0de3f580-8c7f-11ea-8bc8-c527e78d9e04.png)

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

Travis CI build 可以通过

.addParameter(THREAD_POOL_PREFIX_PARAM_NAME, "test")
                .addParameter(THREAD_POOL_SIZE_PARAM_NAME, 10)
                .addParameter(THREAD_POOL_KEEP_ALIVE_TIME_PARAM_NAME, 100);
        AbstractDynamicConfiguration configuration = new AbstractDynamicConfiguration(url) {
            @Override
            protected String doGetConfig(String key, String group) throws Exception {
                return null;
            }
            @Override
            protected void doClose() throws Exception {
            }
        };
        ThreadPoolExecutor threadPoolExecutor = configuration.getWorkersThreadPool();
        ThreadFactory threadFactory = threadPoolExecutor.getThreadFactory();
        Thread thread = threadFactory.newThread(() -> {
        });
        assertEquals(10, threadPoolExecutor.getCorePoolSize());
        assertEquals(10, threadPoolExecutor.getMaximumPoolSize());
        assertEquals(100, threadPoolExecutor.getKeepAliveTime(TimeUnit.MILLISECONDS));
        assertEquals("test-thread-1", thread.getName());
    }
    @Test
    public void testPublishConfig() {
        assertThrows(UnsupportedOperationException.class, () -> configuration.publishConfig(null, null), "No support");
        assertThrows(UnsupportedOperationException.class, () -> configuration.publishConfig(null, null, null), "No support");
    }
    @Test
    public void testGetConfigKeys() {
        assertThrows(UnsupportedOperationException.class, () -> configuration.getConfigKeys(null), "No support");
    }