### 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)


assertEquals(10, parent.getAge());
        assertEquals("jerry", parent.getName());
        assertEquals("haha", parent.getChild().getToy());
        assertSame(parent, parent.getChild().getParent());
        Object[] objects = PojoUtils.realize(new Object[]{generalize}, new Class[]{List.class}, new Type[]{getType("getListGenericType")});
        assertTrue(((List) objects[0]).get(0) instanceof Parent);
    }
    @Test
    public void test_PojoInList() throws Exception {
        Parent p = new Parent();
        p.setAge(10);
        p.setName("jerry");
        List<Object> list = new ArrayList<Object>();
        list.add(p);
        Object generalize = PojoUtils.generalize(list);
        @SuppressWarnings("unchecked")
        List<Object> realize = (List<Object>) PojoUtils.realize(generalize, List.class, getType("getListGenericType"));
        Parent parent = (Parent) realize.get(0);
        assertEquals(10, parent.getAge());
        assertEquals("jerry", parent.getName());
    }
    public void setLong(long l) {
    }
    public void setInt(int l) {
    }
    public List<Parent> getListGenericType() {
        return null;
    }
    public Map<String, Parent> getMapGenericType() {
        return null;