Attempt to invoke virtual method

Good morning, I was doing a generic class to use AlertDialog, but I came across the following problem:

05-28 10:11:16.323 19359-19359/com.example.vitordalmolin.abllock E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.vitordalmolin.abllock, PID: 19359
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
    at android.content.ContextWrapper.getResources(ContextWrapper.java:92)
    at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)
    at android.support.v7.app.AppCompatActivity.getResources(AppCompatActivity.java:542)
    at com.example.vitordalmolin.abllock.additional.SystemStatus.alertDialog(SystemStatus.java:40)
    at com.example.vitordalmolin.abllock.activities.Main2Activity$2.onItemClick(Main2Activity.java:156)
    at android.widget.AdapterView.performItemClick(AdapterView.java:346)
    at android.widget.AbsListView.performItemClick(AbsListView.java:1577)
    at android.widget.AbsListView$PerformClick.run(AbsListView.java:3970)
    at android.widget.AbsListView.onTouchUp(AbsListView.java:6080)
    at android.widget.AbsListView.onTouchEvent(AbsListView.java:5839)
    at android.view.View.dispatchTouchEvent(View.java:10018)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2833)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2504)
    at android.widget.AbsListView.dispatchTouchEvent(AbsListView.java:5771)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.widget.ScrollView.dispatchTouchEvent(ScrollView.java:733)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2844)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2519)
    at com.android.internal.policy.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2869)
    at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1861)
    at android.app.Activity.dispatchTouchEvent(Activity.java:3061)
    at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:68)
    at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:68)
    at com.android.internal.policy.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2830)
    at android.view.View.dispatchPointerEvent(View.java:10253)
    at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:5523)
    at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:5359)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4804)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4857)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4823)
    at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4964)
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4831)
    at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:5021)

This is my method:

public void alertDialog(int title,int mensage, int textPositiveButton, int textNegativeButton, int textNeutralButton){

    Resources res = getResources();
    String localTitle            = String.format(res.getString(title));
    String localmensage          = String.format(res.getString(mensage));
    String localPositiveButton   = "";
    String localNegativeButton   = "";
    String localNeutralButton   = "";
    if(textPositiveButton != 0){
        localPositiveButton   = String.format(res.getString(textPositiveButton));
    }
    if(textNegativeButton != 0){
        localNegativeButton   = String.format(res.getString(textNegativeButton));
    }
    if(textNeutralButton != 0){
        localNeutralButton   = String.format(res.getString(textNeutralButton));
    }


    //Cria o gerador do AlertDialog
    AlertDialog.Builder builder = new AlertDialog.Builder(context, R.style.DialogStyle);
    //define o titulo
    builder.setTitle(localTitle);
    //define a mensagem
    builder.setMessage(localmensage);
    //define um botão como positivo
    builder.setPositiveButton(localPositiveButton, new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {
            alertDialogOption(1);
        }
    });
    //define um botão como negativo.
    builder.setNegativeButton(localNegativeButton, new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {
            //Toast.makeText(BluetoothActivity.this, "negativo=" + arg1, Toast.LENGTH_SHORT).show();
            alertDialogOption(0);
        }
    });
    builder.setNeutralButton(localNeutralButton, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            alertDialogOption(-1);
        }
    });
    //cria o AlertDialog
    alerta = builder.create();
    //Exibe
    alerta.show();
}

And these are the libraries used:

import android.content.Context;
import android.content.DialogInterface;
import android.content.res.Resources;
import android.net.ConnectivityManager;
import android.net.ConnectivityManager;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.widget.Toast;