### 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)


bigPerson = new BigPerson();
        bigPerson.setPersonId("id1");
        bigPerson.setLoginName("name1");
        bigPerson.setStatus(PersonStatus.ENABLED);
        bigPerson.setEmail("abc@123.com");
        bigPerson.setPenName("pname");
        ArrayList<Phone> phones = new ArrayList<Phone>();
        Phone phone1 = new Phone("86", "0571", "11223344", "001");
        Phone phone2 = new Phone("86", "0571", "11223344", "002");
        phones.add(phone1);
        phones.add(phone2);
        PersonInfo pi = new PersonInfo();
        pi.setPhones(phones);
        Phone fax = new Phone("86", "0571", "11223344", null);
        pi.setFax(fax);
        FullAddress addr = new FullAddress("CN", "zj", "1234", "Road1", "333444");
        pi.setFullAddress(addr);
        pi.setMobileNo("1122334455");
        pi.setMale(true);
        pi.setDepartment("b2b");
        pi.setHomepageUrl("www.abc.com");
        pi.setJobTitle("dev");
        pi.setName("name2");
        bigPerson.setInfoProfile(pi);
    }
    private static Child newChild(String name, int age) {
        Child result = new Child();
        result.setName(name);
        result.setAge(age);
        return result;