Resource JSON serialization produce empty "content" property

Hi,

here is my controller code:

@RequestMapping(value= "/test-resource", method = RequestMethod.GET)
public TestResource test() {
    return new TestResource(new Test());
}

private class TestResource extends Resource<Test> {
    public TestResource(Test content, Link... links) {
        super(content, links);
    }
}

private class Test {}

And I use the MappingJackson2HttpMessageConverter as an ObjectMapper.

The result of requesting my controller's method is:

{
    "content": {

    }
}

But in case of Test class is an @Entity or a @Component, it serialized correctly:

{ }

The reason of such behaviour is that Jackson uses UnwrappingBeanSerializer to serialize @Entity and unwrap "content" property, but in case of POJO Jackson uses UnknownSerializer that serialize content as is.

The problem can be solved by setting @JsonSerialize(include = JsonSerialize.Inclusion.NON_EMPTY) class annotation on TestMixIn, but it looks like a hack.