title: notifyDataSetChanged() NullPointerException
body: <p>i try to add onClick this button then create contact in database</p>
  
  <p>Here is code i try to add it to main_fragment</p>
  
  <pre><code>  final Button addBtn = (Button) view.findViewById(R.id.btnadd);
      addBtn.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              Uri imageUri = Uri.parse("android.resource://org.intracode.contactmanager/drawable/no_user_logo.png");
              import_fragment.Contact contact = new import_fragment.Contact(dbHandler.getContactsCount(), String.valueOf(nametxt.getText()), String.valueOf(phoneTxt.getText()), String.valueOf(emailTxt.getText()), String.valueOf(addressTxt.getText()), imageUri);
              if (!contactExists(contact)) {
                  dbHandler.createContact(contact);
                  Contacts.add(contact);
                  contactAdapter.notifyDataSetChanged(); // Error in this line
                  Toast.makeText(getActivity().getApplicationContext(), String.valueOf(nametxt.getText()) + " has been added to your Contacts!", Toast.LENGTH_SHORT).show();
                  return;
              }
              Toast.makeText(getActivity().getApplicationContext(), String.valueOf(nametxt.getText()) + " already exists. Please use a different name.", Toast.LENGTH_SHORT).show();
          }
      });
  </code></pre>
  
  <p>When i press this button in my app, 'app has stopped working'</p>
  
  <p>Here is my logcat</p>
  
  <pre><code>01-22 08:31:04.014 29398-29398/com.al3almya.users.al3almya E/AndroidRuntime: FATAL EXCEPTION: main
                                                                           Process: com.al3almya.users.al3almya, PID: 29398
                                                                           java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ArrayAdapter.notifyDataSetChanged()' on a null object reference
                                                                               at com.al3almya.users.al3almya.main_fragment$1.onClick(main_fragment.java:77)
                                                                               at android.view.View.performClick(View.java:4848)
                                                                               at android.view.View$PerformClick.run(View.java:20262)
                                                                               at android.os.Handler.handleCallback(Handler.java:815)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:104)
                                                                               at android.os.Looper.loop(Looper.java:194)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5637)
                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                               at java.lang.reflect.Method.invoke(Method.java:372)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
  </code></pre>