@Managedproperty in a Managed Bean class returning null

Question

I am trying to inject a Managed Property in my class, but whenever I try to access it in a method annotated with @PostConstruct it returns me null thus generating an Exception.

Follow down my class:

package br.com.pathfind.importacao.managedbean;

import java.io.Serializable;

import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;
import javax.faces.bean.ViewScoped;

import br.com.lantech.pathfind.corporativo.service.ParametroService;
import br.com.lantech.pathfind.model.Parametro;
import br.com.lantech.pathfind.model.exception.PathfindException;

@ManagedBean(name = "importarArquivoBean")
@ViewScoped
public class ImportarArquivoBean implements Serializable {

    private static final long serialVersionUID = 1L;

    private Parametro parametroERP;

    @ManagedProperty("#{parametroService}")
    private ParametroService parametroService;

    private boolean promax;

    @PostConstruct
    private void inicializar() {
        //parametroService retornando nulo.
        try {
            parametroERP = parametroService.recuperaPorDescricao("ERP");
        } catch (PathfindException e) {
            e.printStackTrace();
        }
        promax = false;
        if (parametroERP.getValor().equalsIgnoreCase("PROMAX")) {
            promax = true;
        }
    }

    public boolean deveExibirSAP() {
        return getParametroERP().getValor().equalsIgnoreCase("SAP");
    }

    public Parametro getParametroERP() {
        return parametroERP;
    }

    public void setParametroERP(Parametro parametroERP) {
        this.parametroERP = parametroERP;
    }

    public ParametroService getParametroService() {
        return parametroService;
    }

    public void setParametroService(ParametroService parametroService) {
        this.parametroService = parametroService;
    }

    public boolean isPromax() {
        return promax;
    }

    public void setPromax(boolean promax) {
        this.promax = promax;
    }
}

Does anyone have any idea what it might be? Grateful