Java EJB API REST - Handling Exceptions Databse PostgreSQL

I am continuing a project that I have not started and I have to follow some guidelines. I'm having problems with exception handling, I put the code and then I ask:

The project consists of several "projects in Java", I will name only those that I think are necessary for my question: gps-EJB, gps-persistence, gps-common, gps-war.

Within the gps-wat project I have this class, it is responsible for collecting the requests that come to the API:

@Path("user")
//@Stateless
@javax.enterprise.context.RequestScoped
public class UserResource {

private static final Logger LOGGER = LoggerFactory.getLogger  (Constants.LOGGER_NAME);


@Context
private UriInfo context;

@Inject
private UserEJBLocal userEJB;

/**
 * Creates a new instance of LocationResource
 */
public UserResource() {
}

@Path("/new")
@PUT
@Produces("application/json")
@Consumes("application/json")
public Response createUser(DBUser user) {
    System.out.println("createuser");
    try {
        userEJB.createUser(user);
        DBUser userinsert = userEJB.getUser (String.valueOf(user.getUserId()));
        DBUserResponse response = new DBUserResponse(userinsert);
        return Response.ok(response).build();
    } catch(Throwable ex) {
        LOGGER.error(ex.getMessage(), ex);
        //TODO manejar excepciones del ejb, no Throwable; usar codigos de estado http
        DBUserResponse response = new DBUserResponse(ErrorCode.E001.toString());
        return Response.status(Response.Status.CONFLICT).entity(response).build();    

    }
    //TODO manejar excepciones
}

Mainly the problem I have here, what I want is that when there is an error in the "try" between the catch and I have the correct information the exception.

The corresponding EJB class is the following:

@Stateless(name=UserEJBLocal.EJB_NAME)
public class UserEJB implements UserEJBLocal{

private static final org.slf4j.Logger LOGGER = LoggerFactory.getLogger(UserEJB.class);

@PostConstruct
public void init() {
    String description = "You are in UserEJB class";
    LOGGER.info(description);
}

@Override
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public void createUser(DBUser user) {
    LOGGER.info("createUser(AN_USER)");
    LOGGER.info("The user passed by param has the following id: " + user.getUserId());
    UserMapper mapper = new UserMapper();
    try {
        mapper.createUser(user);
    } catch (DatabaseException ex) {
        String description = "createUser(AN_USER) call has an ERROR: ";
        LOGGER.error(description, ex);
        String sqlcod = ex.getSQLState();
        if(sqlcod.equals("23505")){
            try {
                throw new Throwable("error", ex.getCause());
            } catch (Throwable ex1) {
                Logger.getLogger(UserEJB.class.getName()).log(Level.SEVERE, null, ex1);
            }
        }
    }
}

As you can see in this last class I am collecting a BD error (for the case that it is a duplicate entry). I have been debugging, and enters the "catch" of the UserResource class of the corresponding method, but the exception comes to me without information, that is, its empty or null fields: -S

Why is this?