when injecting EntityManager using CDI 2.0 throws java.lang.NullPointerException

问题

@ApplicationScoped
public class PersonDao {

    @PersistenceContext
    private EntityManager entityManager;

    public List<Person> getAllPersons()
    {  
        Query query=entityManager.createQuery("SELECT p FROM PersonEntity p");
        List<Person> persons=query.getResultList();
        return persons; 
    }
}

Can you please help.. Thanks

来源：https://stackoverflow.com/questions/59541849/when-injecting-entitymanager-using-cdi-2-0-throws-java-lang-nullpointerexception