### 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)


assertObject(new Person());
        assertObject(new SerializablePerson());
    }
    @Test
    public void test_has_no_nullary_constructor_pojo() {
        assertObject(new User(1,"fibbery"));
    }
    @Test
    public void test_Map_List_pojo() throws Exception {
        Map<String, List<Object>> map = new HashMap<String, List<Object>>();
        List<Object> list = new ArrayList<Object>();
        list.add(new Person());
        list.add(new SerializablePerson());
        map.put("k", list);
        Object generalize = PojoUtils.generalize(map);
        Object realize = PojoUtils.realize(generalize, Map.class);
        assertEquals(map, realize);
    }
    @Test
    public void test_PrimitiveArray() throws Exception {
        assertObject(new boolean[]{true, false});
        assertObject(new Boolean[]{true, false, true});
        assertObject(new byte[]{1, 12, 28, 78});
        assertObject(new Byte[]{1, 12, 28, 78});
        assertObject(new char[]{'a', '中', '无'});
        assertObject(new Character[]{'a', '中', '无'});
        assertObject(new short[]{37, 39, 12});
        assertObject(new Short[]{37, 39, 12});
        assertObject(new int[]{37, -39, 12456});
        assertObject(new Integer[]{37, -39, 12456});