### 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 dest;
            }
        }
        if (pojo instanceof Map<?, ?> && type != null) {
            Object className = ((Map<Object, Object>) pojo).get("class");
            if (className instanceof String) {
                try {
                    type = ClassUtils.forName((String) className);
                } catch (ClassNotFoundException e) {
                    
                }
            }
            
            if (type.isEnum()) {
                Object name = ((Map<Object, Object>) pojo).get("name");
                if (name != null) {
                    return Enum.valueOf((Class<Enum>) type, name.toString());
                }
            }
            Map<Object, Object> map;
            
            if (!type.isInterface() && !type.isAssignableFrom(pojo.getClass())) {
                try {
                    map = (Map<Object, Object>) type.newInstance();
                    Map<Object, Object> mapPojo = (Map<Object, Object>) pojo;
                    map.putAll(mapPojo);
                    if (GENERIC_WITH_CLZ) {
                        map.remove("class");
                    }
                } catch (Exception e) {