### 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)


void sayHello(String name);
    Set<String> keys(Map<String, String> map);
    String echo(String text);
    Map echo(Map map);
    long timestamp();
    String getThreadName();
    int getSize(String[] strs);
    int getSize(Object[] os);
    Object invoke(String service, String method) throws Exception;
    int stringLength(String str);
    Type enumlength(Type... types);
    Type getType(Type type);
    String get(CustomArgument arg1);
    byte getbyte(byte arg);
    void nonSerializedParameter(NonSerialized ns);
    NonSerialized returnNonSerialized();
    long add(int a, long b);
    int getPerson(Person person);
    int getPerson(Person person1, Person perso2);
    String getPerson(Man man);
    String getRemoteApplicationName();
}