- [ ] 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

@Test
    public void testGetConfig() {
        assertNull(configuration.getConfig(null, null));
        assertNull(configuration.getConfig(null, null, 200));
    }
    @Test
    public void testGetInternalProperty() {
        assertNull(configuration.getInternalProperty(null));
    }
    @Test
    public void testGetProperties() {
        assertNull(configuration.getProperties(null, null));
        assertNull(configuration.getProperties(null, null, 100L));
    }
    @Test
    public void testAddListener() {
        configuration.addListener(null, null);
        configuration.addListener(null, null, null);
    }
    @Test
    public void testRemoveListener() {
        configuration.removeListener(null, null);
        configuration.removeListener(null, null, null);
    }
    @Test
    public void testClose() throws Exception {
        configuration.close();
    }
}