### 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)


private static final Logger logger = LoggerFactory.getLogger(PojoUtils.class);
    private static final ConcurrentMap<String, Method> NAME_METHODS_CACHE = new ConcurrentHashMap<String, Method>();
    private static final ConcurrentMap<Class<?>, ConcurrentMap<String, Field>> CLASS_FIELD_CACHE = new ConcurrentHashMap<Class<?>, ConcurrentMap<String, Field>>();
    private static final boolean GENERIC_WITH_CLZ = Boolean.parseBoolean(ConfigUtils.getProperty(CommonConstants.GENERIC_WITH_CLZ_KEY,"true"));
    public static Object[] generalize(Object[] objs) {
        Object[] dests = new Object[objs.length];
        for (int i = 0; i < objs.length; i++) {
            dests[i] = generalize(objs[i]);
        }
        return dests;
    }
    public static Object[] realize(Object[] objs, Class<?>[] types) {
        if (objs.length != types.length) {
            throw new IllegalArgumentException("args.length != types.length");