### 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 new HashSet<Object>(len);
        }
        if (!type.isInterface() && !Modifier.isAbstract(type.getModifiers())) {
            try {
                return (Collection<Object>) type.newInstance();
            } catch (Exception e) {
                
            }
        }
        return new ArrayList<Object>();
    }
    private static Map createMap(Map src) {
        Class<? extends Map> cl = src.getClass();
        Map result = null;
        if (HashMap.class == cl) {
            result = new HashMap();
        } else if (Hashtable.class == cl) {
            result = new Hashtable();
        } else if (IdentityHashMap.class == cl) {
            result = new IdentityHashMap();
        } else if (LinkedHashMap.class == cl) {
            result = new LinkedHashMap();
        } else if (Properties.class == cl) {
            result = new Properties();
        } else if (TreeMap.class == cl) {
            result = new TreeMap();
        } else if (WeakHashMap.class == cl) {
            return new WeakHashMap();
        } else if (ConcurrentHashMap.class == cl) {
            result = new ConcurrentHashMap();