Jersey response.readEntity(...) sometimes returns null - jackson

Question

Consider this snippet from my REST client (Jersey 2.26). It's used to post objects and return the response object. If the REST server returns an error (status >= 400), then instead of returning an entity of type T I want to read an entity of type ErrorMessage and throw an exception containing the error message object.
protected <T> T post(final Class<T> type,
final Object entity,
final Map<String, Object> queryParams,
final String methodPath,
final Object... arguments) {
return postResponse(
getInvocationBuilderJson(methodPath,
queryParams,
arguments),
entity
).readEntity(type);
}
protected Response postResponse(final Invocation.Builder invocationBuilder,
final Object entity) {
return handleErrors(
invocationBuilder.post(Entity.entity(entity,
MediaType.APPLICATION_JSON_TYPE))
);
}
protected Response handleErrors(final Response response) {
if (response.getStatus() >= 400) {
throw new InvocationException(response.readEntity(ErrorMessage.class));
}
return response;
}
If no error occurs (status < 400), then my object of type T is returned as expected. However, when an error does occur, response.readEntity(ErrorMessage.class) returns null. But (and this is the strange part), this does get me data (at the handleErrors method):
byte[] data = readAllBytes((InputStream) response.getEntity());
I could use that and deserialize it manually.. but I would first like to know if there are any options to fix this without implementing workarounds.

Answer 1

After switching from the default MOXy JSON (de)serializer (we now are using a GSON provider) the problem was resolved.
We recently had a similar issue with JSON-B. There is turned out we had to add a getter and setter on our error object on order to (de)serialize the object.