### 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)


String[] values = new String[len];
            for (int i = 0; i < len; i++) {
                values[i] = ((Enum<?>) Array.get(pojo, i)).name();
            }
            return values;
        }
        if (ReflectUtils.isPrimitives(pojo.getClass())) {
            return pojo;
        }
        if (pojo instanceof Class) {
            return ((Class) pojo).getName();
        }
        Object o = history.get(pojo);
        if (o != null) {
            return o;
        }
        history.put(pojo, pojo);
        if (pojo.getClass().isArray()) {
            int len = Array.getLength(pojo);
            Object[] dest = new Object[len];
            history.put(pojo, dest);
            for (int i = 0; i < len; i++) {
                Object obj = Array.get(pojo, i);
                dest[i] = generalize(obj, history);
            }
            return dest;
        }
        if (pojo instanceof Collection<?>) {
            Collection<Object> src = (Collection<Object>) pojo;
            int len = src.size();