How to not display the empty field retreived from Parse.com in listview

Question

I have Created Three Columns "class1" "class2 "class3" in parse server. and retrieving each column to different activity. table

some table fields are empty. So when i retrieve it displays empty field in listview and gives an error "Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference" for undefined field

I know i can just create different classes for each column and retrieve but wondering is there any way to not display the empty field in listview.

Activity.java

    public class topics_class1 extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_topics_class1);

        final ArrayList<String> topics1 = new ArrayList<>();

        final ListView listView = findViewById(R.id.listView_topics_class1);
        final ArrayAdapter arrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, topics1);

        ParseQuery<ParseObject> query = ParseQuery.getQuery("Topics");
        query.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> objects, ParseException e) {
                if (e == null){
                    for (ParseObject topic : objects){

                        topics1.add(topic.getString("class_2"));

                    }
                    listView.setAdapter(arrayAdapter);

                    }
                else {
                    e.printStackTrace();
                }
            }

        });      
    }
}

Answer 1

Just skip empty values.

String text = topic.getString("class_2");
if(text != null && !text.isEmpty()) {
    //topics1.add(..
}

Update: if you need "empty cell" then assign empty string instead of null:

topics1.add("");