I'm working on a small application with seam framework and I'm having trouble when I use the command entityManager.persist (usuario);
the server returns NullPointerException in method usuarioAction.salvarUsuario() why?

20:33:05,018 ERROR [application] java.lang.NullPointerException
javax.faces.el.EvaluationException: java.lang.NullPointerException



Myclass UsuarioAction.java

import java.util.List;
import javax.persistence.EntityManager;
import org.jboss.seam.ScopeType;
import org.jboss.seam.annotations.In;
import org.jboss.seam.annotations.Name;
import org.jboss.seam.annotations.Out;
import org.jboss.seam.annotations.Scope;
import org.jboss.seam.annotations.datamodel.DataModel;
import org.jboss.seam.annotations.datamodel.DataModelSelection;
import org.jboss.seam.faces.FacesMessages;
import org.jboss.seam.international.StatusMessage.Severity;

import br.odebrecht.entity.Usuario;

@Name("usuarioAction")
@Scope(ScopeType.CONVERSATION)
public class UsuarioAction {

@In(required=false)
@Out(required=false)
private Usuario usuario;

@In
private EntityManager entityManager;

@Out
FacesMessages facesMessages;

@DataModel
List<Usuario> listaUsuario;

@DataModelSelection
@Out(required=false)
Usuario usuarioSelecionado;

public void salvarUsuario(){
try {
entityManager.persist(usuario); //Here NullPointerException happens

} catch (Exception e) {
facesMessages.add(Severity.ERROR,"Erro ao salvar informações!!! ");
}
facesMessages.add(Severity.INFO,"Operação realizada com sucesso!!!");
}
}



usuario.xhtml call the salvarUsuario method

<h:commandButton id="salvar" action="#{usuarioAction.salvarUsuario}" value="Salvar" />


Someone help me ..

thanks for attention