onPostExecute causing application to crash

onPostExecute causing application to crash

Below is my onPostExecute method. When my AsyncTask fires it does
everything that it suppose to do but when it tries to execute my
onPostExecute my application crashes and I get this message in my logcat
09-14 22:45:22.481: E/AndroidRuntime(1141): FATAL EXCEPTION: main
09-14 22:45:22.481: E/AndroidRuntime(1141): java.lang.NullPointerException
09-14 22:45:22.481: E/AndroidRuntime(1141): at
com.testapp1.ListView$LoadAllData.onPostExecute(ListView.java:193)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
com.testapp1.ListView$LoadAllData.onPostExecute(ListView.java:1)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
android.os.AsyncTask.finish(AsyncTask.java:631)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
android.os.AsyncTask.access$600(AsyncTask.java:177)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
android.os.Handler.dispatchMessage(Handler.java:99)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
android.os.Looper.loop(Looper.java:137)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
android.app.ActivityThread.main(ActivityThread.java:5041)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
java.lang.reflect.Method.invokeNative(Native Method)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
java.lang.reflect.Method.invoke(Method.java:511)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
09-14 22:45:22.481: E/AndroidRuntime(1141): at
dalvik.system.NativeStart.main(Native Method)
this is my onPostExecute method
@Override
protected void onPostExecute(String file_URL) {
if(file_URL.equals("0")) {
pDialog.dismiss();
Toast.makeText(ListView.this, "No data found",
Toast.LENGTH_SHORT).show();
finish();
}else{
if (pDialog != null && pDialog.isShowing()) pDialog.dismiss();
ListAdapter adapter = new SimpleAdapter(getBaseContext(),
questionList,
R.layout.listelements,
new String[] { TAG_QUESTION_SUBJECT }, new int[] {
R.id.Subject,});
setListAdapter(adapter);
}}}
May I please have somebody help with this issue that I have.