Registered hibernateModule lead to 'NON_EMPTY' failure

```
public class Mock
{
    private Long id;
    private String name;
    private Set<String> mocks = Sets.newHashSet();
}

new ObjectMapper().registerModule(new Hibernate3Module()).setSerializationInclusion(Include.NON_EMPTY).writeValueAsString(mock)
```
## output

{"mocks":[]}
