### 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)


}
    /**
     * Get parameterized type
     *
     * @param genericType generic type
     * @param index       index of the target parameterized type
     * @return Return Person.class for List<Person>, return Person.class for Map<String, Person> when index=0
     */
    private static Type getGenericClassByIndex(Type genericType, int index) {
        Type clazz = null;
        
        if (genericType instanceof ParameterizedType) {
            ParameterizedType t = (ParameterizedType) genericType;
            Type[] types = t.getActualTypeArguments();
            clazz = types[index];
        }
        return clazz;
    }
    private static Object newInstance(Class<?> cls) {
        try {
            return cls.newInstance();
        } catch (Throwable t) {
            try {
                Constructor<?>[] constructors = cls.getDeclaredConstructors();
                /**
                 * From Javadoc java.lang.Class#getDeclaredConstructors
                 * This method returns an array of Constructor objects reflecting all the constructors
                 * declared by the class represented by this Class object.
                 * This method returns an array of length 0,
                 * if this Class object represents an interface, a primitive type, an array class, or void.