Null pointer access in variable inside a for

Question

In the lines marked with $ show the following message:

Multiple markers at this line - Null pointer access: The variable InformeSalvaguardasAGR can only be null at this location - Null pointer access: The variable InformeSalvaguardasAGR can only be null at this location

But i dont know why exactly, InformeAmenazasAGR is a superior variable and they can access. Why shows this message and how i can i make it correctly?

            List<Object> InformeAmenazasAGR = null;
            List<Object> InformeSalvaguardasAGR = null;
            try {
                Locale locale = (Locale)request.getSession().getAttribute(Globals.LOCALE_KEY);
                if (locale == null){
                    locale = Locale.getDefault();
                }
                ResourceBundle recursos = ResourceBundle.getBundle(ProcopGlobals.FICHERO_MULTILENGUAJE,locale);
                manager = new AGRInformesManager();

                // EXTRAER TODAS LAS AMENAZAS.          
                InformeAmenazasAGR = manager.preparaInformeRiesgoActivos(idDimension, tipoActivo, idActivo, tipoActivoTexto, nombreActivo, recursos);

                for (int i = 0; i < InformeAmenazasAGR.size()-1; i++) {
                    String Amenaza = InformeAmenazasAGR.get(i).toString();
                    Amenaza = Amenaza.substring(1,3);
                    Object resultadoQuery = manager.SalvaguardaPorAmenaza(Amenaza);
                    if(resultadoQuery!= null){
    $                   InformeSalvaguardasAGR.add(resultadoQuery);
                    } else {

                    }                           
                }
                if (InformeSalvaguardasAGR != null) {
                    //Prueba
                    String informetexto =InformeSalvaguardasAGR.toString();
                }

            } catch( Exception e ) {
                log.error( "No fue posible generar el informe AGR para el Tipo: "+tipoActivo+" Activo: "+idActivo+" en Dimension: "+idDimension+".EX:" + e.toString());
                e.printStackTrace();
            } finally {
                if( manager != null ) {
                    try {
                        manager.closeDAO();
                    } catch( Exception e ) {
                        e.printStackTrace();
                }
                manager = null;
            }
        }
    JSONArray JSonArray = new JSONArray();
    JSonArray.put(InformeSalvaguardasAGR);
    String InformeSalvasAGR = JSonArray.toString();
    InformeSalvasAGR = InformeSalvasAGR.substring(1, InformeSalvasAGR.length()-1);

    request.setAttribute("InformeAmenazasAGR", InformeSalvasAGR);

Thank you in advance.

Answer 1

Though it is global it is never initialized. You cannot add to a list which is null. So initialize the list to :

List<Object> InformeSalvaguardasAGR = new ArrayList<Object>();

instead of

List<Object> InformeSalvaguardasAGR = null;

Answer 2

If something happens at the try-catch-finally block, both InformeSalvaguardasAGR and InformeAmenazasAGR won't be initialized and remain null . In future if they are null , you can get NPE trying to call their methods. I suggest you to replace this:

List<Object> InformeAmenazasAGR = null;
List<Object> InformeSalvaguardasAGR = null;

with this:

List<Object> InformeAmenazasAGR = new ArrayList<Object>();
List<Object> InformeSalvaguardasAGR = new ArrayList<Object>();