Maven/JSF - HTTP Status 500 – Internal Server Error - Could not initialize class br.com.listatarefa.dao.DAO

Question

package br.com.listatarefa.dao;

import java.io.Serializable;

import java.util.List;

import javax.persistence.Query;

import javax.persistence.EntityManager;

import br.com.listatarefa.model.Base;

public class DAO implements Serializable {

private static final long serialVersionUID = 1L;
private static EntityManager manager = ConnectionFactory.getEntityManager();

public T buscarPorId(Class<T> clazz, Long id) {
    return manager.find(clazz, id);
}

public void salvar(T t) {
    try {   
        manager.getTransaction().begin();
        if(t.getId() == null) {
            manager.persist(t);
        }
        else {
            manager.merge(t);
        }
        manager.getTransaction().commit();
    }
    catch (Exception e){
        manager.getTransaction().rollback();
    }
}

public void remover(Class<T> clazz, Long id) {
    T t = buscarPorId(clazz, id);
    try {   
        manager.getTransaction().begin();
        manager.remove(t);
        manager.getTransaction().commit();
    }
    catch (Exception e){
        manager.getTransaction().rollback();
    }
}

@SuppressWarnings("unchecked")
public List<T> buscarTodos(String jpql){
    Query query = manager.createQuery(jpql);
    return query.getResultList();
}

}