### 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)


}
    public void assertObject(Object data) {
        assertObject(data, null);
    }
    public void assertObject(Object data, Type type) {
        Object generalize = PojoUtils.generalize(data);
        Object realize = PojoUtils.realize(generalize, data.getClass(), type);
        assertEquals(data, realize);
    }
    public <T> void assertArrayObject(T[] data) {
        Object generalize = PojoUtils.generalize(data);
        @SuppressWarnings("unchecked")
        T[] realize = (T[]) PojoUtils.realize(generalize, data.getClass());
        assertArrayEquals(data, realize);
    }
    @Test
    public void test_primitive() throws Exception {
        assertObject(Boolean.TRUE);
        assertObject(Boolean.FALSE);
        assertObject(Byte.valueOf((byte) 78));
        assertObject('a');
        assertObject('中');
        assertObject(Short.valueOf((short) 37));
        assertObject(78);
        assertObject(123456789L);
        assertObject(3.14F);
        assertObject(3.14D);
    }
    @Test
    public void test_pojo() throws Exception {