lower version, for example 2.6.8
```properties
dubbo.provider.version=1.0
```

2.7.6 failed to recognize the provider url with 'default.version=1.0' key,  it only takes 'version.1.0' into consideration.

@Test
    public void testParseUrlsAddressNull() {
        assertNull(UrlUtils.parseURLs(null, null));
    }
    @Test
    public void testConvertRegister() {
        String key = "perf/dubbo.test.api.HelloService:1.0.0";
        Map<String, Map<String, String>> register = new HashMap<String, Map<String, String>>();
        register.put(key, null);
        Map<String, Map<String, String>> newRegister = UrlUtils.convertRegister(register);
        assertEquals(register, newRegister);
    }
    @Test
    public void testConvertRegister2() {
        String key = "dubbo.test.api.HelloService";
        Map<String, Map<String, String>> register = new HashMap<String, Map<String, String>>();
        Map<String, String> service = new HashMap<String, String>();
        service.put("dubbo://127.0.0.1:20880/com.xxx.XxxService", "version=1.0.0&group=test&dubbo.version=2.0.0");
        register.put(key, service);
        Map<String, Map<String, String>> newRegister = UrlUtils.convertRegister(register);
        Map<String, String> newService = new HashMap<String, String>();
        newService.put("dubbo://127.0.0.1:20880/com.xxx.XxxService", "dubbo.version=2.0.0&group=test&version=1.0.0");
        assertEquals(newService, newRegister.get("test/dubbo.test.api.HelloService:1.0.0"));
    }
    @Test
    public void testSubscribe() {
        String key = "perf/dubbo.test.api.HelloService:1.0.0";
        Map<String, String> subscribe = new HashMap<String, String>();
        subscribe.put(key, null);
        Map<String, String> newSubscribe = UrlUtils.convertSubscribe(subscribe);