### 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)


Child c = new Child();
        c.setToy("haha");
        p.setChild(c);
        c.setParent(p);
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("k", p);
        Object generalize = PojoUtils.generalize(map);
        @SuppressWarnings("unchecked")
        Map<String, Object> realize = (Map<String, Object>) PojoUtils.realize(generalize, Map.class, getType("getMapGenericType"));
        Parent parent = (Parent) realize.get("k");
        assertEquals(10, parent.getAge());
        assertEquals("jerry", parent.getName());
        assertEquals("haha", parent.getChild().getToy());
        assertSame(parent, parent.getChild().getParent());
    }
    @Test
    public void test_LoopPojoInList() throws Exception {
        Parent p = new Parent();
        p.setAge(10);
        p.setName("jerry");
        Child c = new Child();
        c.setToy("haha");
        p.setChild(c);
        c.setParent(p);
        List<Object> list = new ArrayList<Object>();
        list.add(p);
        Object generalize = PojoUtils.generalize(list);
        @SuppressWarnings("unchecked")
        List<Object> realize = (List<Object>) PojoUtils.realize(generalize, List.class, getType("getListGenericType"));
        Parent parent = (Parent) realize.get(0);