### Environment

* Dubbo version: 2.7.4.1
* Operating System version: macOS Catalina Version 10.15.3
* Java version: 1.8.0_231

### Steps to reproduce this issue

1. 通过telnet调用接口如下
方法(Method)
`public String convert7(UserInfoCondition userInfoCondition) {  }`
参数(Parameter)
`public class UserInfoCondition {
    private List<Map<Integer, UserInfo>> userList;
}`
`public class UserInfo {
    private String accountMobile;
    private String userPassword;
}`

invoke UsesrInfoFacade.convert7({"userList":[{"1":{"accountMobile":"15052234567"}}]})
or
invoke UsesrInfoFacade.convert7({"userList":[{1:{"accountMobile":"15052234567"}}]})

提示如下错误(has a problem)
![image](https://user-images.githubusercontent.com/17045745/77892951-ebd50d00-72a5-11ea-95b0-dd59a68a83cc.png)

到底如何书写这个入参呢?(How to write the parameters)


@Test
    public void testRealize() throws Exception {
        Map<String, String> map = new LinkedHashMap<String, String>();
        map.put("key", "value");
        Object obj = PojoUtils.generalize(map);
        assertTrue(obj instanceof LinkedHashMap);
        Object outputObject = PojoUtils.realize(map, LinkedHashMap.class);
        assertTrue(outputObject instanceof LinkedHashMap);
        Object[] objects = PojoUtils.realize(new Object[]{map}, new Class[]{LinkedHashMap.class});
        assertTrue(objects[0] instanceof LinkedHashMap);
        assertEquals(objects[0], outputObject);
    }
    @Test
    public void testRealizeLinkedList() throws Exception {
        LinkedList<Person> input = new LinkedList<Person>();
        Person person = new Person();
        person.setAge(37);
        input.add(person);
        Object obj = PojoUtils.generalize(input);
        assertTrue(obj instanceof List);
        assertTrue(input.get(0) instanceof Person);
        Object output = PojoUtils.realize(obj, LinkedList.class);
        assertTrue(output instanceof LinkedList);
    }
    @Test
    public void testPojoList() throws Exception {
        ListResult<Parent> result = new ListResult<Parent>();
        List<Parent> list = new ArrayList<Parent>();
        Parent parent = new Parent();
        parent.setAge(Integer.MAX_VALUE);