Hibernate LazyInitializationException

I have a problem with my java project when I execute a function generated by the hibernate it returns it correctly, but if I try to access an instance object of another generated class it gives me an error because this is null

The function where the error jumps is this:

public List<Object> verificarUsuario(String user, String pasword) {
     List<Object> result = null;
     Usuarios us = ProveedorServicios.getUsuariosJpaController().findUsuarios(user);

     if(us != null && us.getPasword().equals(pasword)){
        int idUser = us.getIdUsuario();
        result = new ArrayList<>();
        result.add(user);
        List<Integer> roles = new ArrayList<>();
        List<RolesUsuario> rolesUsuario = findRolesUsuarioEntities();
        Iterator<RolesUsuario> iter = rolesUsuario.iterator();

        while(iter.hasNext() && roles.size() < 3){
            RolesUsuario ru = iter.next();

            if(ru.getIdUsuario().getIdUsuario() == idUser)
                roles.add(ru.getIdRol().getIdRol());
        } 

        if(!roles.isEmpty())
            result.add(roles);
        else
            result = null;
    }

    return result;
}

This is the function assigned to:

Usuarios us = ProveedorServicios.getUsuariosJpaController().findUsuarios(user);

public Usuarios findUsuarios(String id) {
    Usuarios user = null;
    List<Usuarios> users = findUsuariosEntities();
    Iterator<Usuarios> iter = users.iterator();

    while(iter.hasNext() && user == null){
        Usuarios us = iter.next();

        if(us.getIdUser().equalsIgnoreCase(id))
            user = us;
    }               

    return user;        
}

This function is generated by the hibernate findRolesUsuarioEntities () (It is the one that returns the list that contains the class that has among its attributes a User type object)

@Entity
@Table(name = "roles_usuario")
@XmlRootElement
@NamedQueries({@NamedQuery(name = "RolesUsuario.findAll", query = "SELECT r FROM RolesUsuario r"), @NamedQuery(name = "RolesUsuario.findByIdRolesUsuario", query = "SELECT r FROM RolesUsuario r WHERE r.idRolesUsuario = :idRolesUsuario")})'
public class RolesUsuario implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id_roles_usuario")
private Integer idRolesUsuario;
@JoinColumn(name = "id_rol", referencedColumnName = "id_rol")
@ManyToOne(optional = false, fetch = FetchType.LAZY)
private Roles idRol;
@JoinColumn(name = "id_usuario", referencedColumnName = "id_usuario")
@ManyToOne(optional = false, fetch = FetchType.LAZY)
private Usuarios idUsuario;

And this is the exception that comes to me

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:164)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:285)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
at modelo.Usuarios_$$_jvst492_a.getIdUsuario(Usuarios_$$_jvst492_a.java)
at servicios.RolesUsuarioJpaController.verificarUsuario(RolesUsuarioJpaController.java:203)