Context has null objects in support class

Question

I try add method in another class which need help me processing errors. And when I need get toast, I get error. How can I decide this situation? Please, help me and explain me how use contexts. Thank you.

This my error:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference

And this my code:

public class DataHelper extends BaseAppCompatActivity {
protected Intent intent;

/**
 * Выводит сумму услуги
 * @param price цена
 * @param discount скидка
 * @return
 */
public static Double Sum (double price, double discount){
    Double sum = null;
    if (price == 0 && discount == 0){
         return null;
    } else if (price == discount){
         sum = price;
    } else if (price > discount || price < discount){
         sum = price - discount;
    }
    return sum;
}

/**
 * Обработка ошибок
 * @param errorCode код ошибки
 * @param errorDescription описание ошибки
 */
public void processingError(String errorCode, String errorDescription){
    switch (errorCode){
        case "inside":
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "method_not_found":
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "method_access_denied":
            intent = new Intent(this, AuthorizationActivity.class);
            startActivity(intent);
            finish();
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "bad_authorization":
            intent = new Intent(this, AuthorizationActivity.class);
            startActivity(intent);
            finish();
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "bad_client_secret_or_id":
            intent = new Intent(this, AuthorizationActivity.class);
            startActivity(intent);
            finish();
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "app_access_denied":
            intent = new Intent(this, AuthorizationActivity.class);
            startActivity(intent);
            finish();
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "wrong_params":
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "wrong_param_value":
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
        case "object_not_found":
            Toast.makeText(getApplicationContext(), errorDescription, Toast.LENGTH_SHORT).show();
            break;
    }
}

}