### 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)


return person;
    }
    public Set<String> keys(Map<String, String> map) {
        return map == null ? null : map.keySet();
    }
    public void nonSerializedParameter(NonSerialized ns) {
    }
    public NonSerialized returnNonSerialized() {
        return new NonSerialized();
    }
    public long add(int a, long b) {
        return a + b;
    }
    @Override
    public int getPerson(Person person) {
        return person.getAge();
    }
    @Override
    public int getPerson(Person person1, Person perso2) {
        return person1.getAge() + perso2.getAge();
    }
    @Override
    public String getPerson(Man man) {
        return man.getName();
    }
    @Override
    public String getRemoteApplicationName() {
        return RpcContext.getContext().getRemoteApplicationName();
    }
}