### 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)


Map map = new HashMap();
        map.put("message", "dubbo exception");
        Object o = PojoUtils.realize(map, RuntimeException.class);
        assertEquals(((Throwable) o).getMessage(), "dubbo exception");
    }
    @Test
    public void testIsPojo() throws Exception {
        assertFalse(PojoUtils.isPojo(boolean.class));
        assertFalse(PojoUtils.isPojo(Map.class));
        assertFalse(PojoUtils.isPojo(List.class));
        assertTrue(PojoUtils.isPojo(Person.class));
    }
    public List<Person> returnListPersonMethod() {
        return null;
    }
    public BigPerson returnBigPersonMethod() {
        return null;
    }
    public Type getType(String methodName) {
        Method method;
        try {
            method = getClass().getDeclaredMethod(methodName, new Class<?>[]{});
        } catch (Exception e) {
            throw new IllegalStateException(e);
        }
        Type gtype = method.getGenericReturnType();
        return gtype;
    }
    @Test
    public void test_simpleCollection() throws Exception {