### 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)


}
        Object[] dests = new Object[objs.length];
        for (int i = 0; i < objs.length; i++) {
            dests[i] = realize(objs[i], types[i]);
        }
        return dests;
    }
    public static Object[] realize(Object[] objs, Class<?>[] types, Type[] gtypes) {
        if (objs.length != types.length || objs.length != gtypes.length) {
            throw new IllegalArgumentException("args.length != types.length");
        }
        Object[] dests = new Object[objs.length];
        for (int i = 0; i < objs.length; i++) {
            dests[i] = realize(objs[i], types[i], gtypes[i]);
        }
        return dests;
    }
    public static Object generalize(Object pojo) {
        return generalize(pojo, new IdentityHashMap<Object, Object>());
    }
    @SuppressWarnings("unchecked")
    private static Object generalize(Object pojo, Map<Object, Object> history) {
        if (pojo == null) {
            return null;
        }
        if (pojo instanceof Enum<?>) {
            return ((Enum<?>) pojo).name();
        }
        if (pojo.getClass().isArray() && Enum.class.isAssignableFrom(pojo.getClass().getComponentType())) {
            int len = Array.getLength(pojo);