NPE injecting service with CDI

I am developing a simple REST application using Java EE 7 with Glasfish 4 as AS for learning purposes and getting an annoying NullPointerException I cannot explain why.

I have a model class:

package com.test.model;

@Entity
@Table(name = "USUARIO")
public class User implements Serializable {
    private String login;

    @Id public String getLogin() {
        return login;
    }
}

A UserApiController class:

package com.test.api.controller;

@Path("/users")
public class UserApiController {
    @Inject private UserService userService;

   @Path("/all") @GET @Produces("application/json")
   public JsonArray getAll() {
       // call to userService.findAll method, raises NPE
   }

(The Persistence class is based on question http://ift.tt/1HgdomQ)

A UserPersistence class that holds the EntityManager:

package com.test.persistence;

@Stateless
public class UserPersistence extends PersistenceFacade<User, String> {

    @PersistenceContext(unitName = "test")
    private EntityManager entityManager;

    public final List<User> findAll() {

        TypedQuery<User> query = entityManager.createQuery("select u from User u", User.class);

        List<User> queryResult = query.getResultList();
        if (queryResult == null) {
            return new ArrayList<User>();
        }

        return queryResult;
    }
}

A UserService class:

package com.test.service;

@Stateless
public class UserService {
    @Inject private UserPersistence userPersistence;

    public final List<User> findAll() {
        return userPersistence.findAll();
    }
}

And finally the ApiConfig class:

package com.test.api;

@ApplicationPath("/api")
public class ApiConfig extends javax.ws.rs.core.Application { }

Also I have a beans.xml file in src/main/resources/META-INF with this content:

<beans xmlns="http://ift.tt/19L2NlC"
   xmlns:xsi="http://ift.tt/ra1lAU"
   xsi:schemaLocation="http://ift.tt/19L2NlC http://ift.tt/18tV3H8"
   version="1.1" bean-discovery-mode="all">
</beans>

When I deploy the project (Maven) and run the server it starts correctly, but when I try to access localhost:8080/test/api/users/all, I get a NPE error when trying to invoke the findAll() method from userService.

Advertencia:   StandardWrapperValve[com.test.api.ApiConfig]: Servlet.service() for servlet com.test.api.ApiConfig threw exception
java.lang.NullPointerException
    at com.test.service.UserService.findAll(UserService.java:21)
    at com.test.api.controller.UserApiController.getAll(UserApiController.java:30)

Debugging I can see that userPersistence field is null when it is accessed. I cannot see why this is null but userService is instantiated correctly, for example.