java.lang.RuntimeException: Layout cannot be null

Question

i am studying this tutorial and i have some problems. I was able to launch my app and share messages to the Firebase database; however, i couldn't see them. But right now, i am getting this error.

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.furka.findit/com.example.furka.findit.ChatActivity}: java.lang.RuntimeException: Layout cannot be null. Call setLayout.

This is my onClick viewListener of send message button:

public void onClick(View view) {
                EditText input = (EditText)findViewById(R.id.input);

                // Read the input field and push a new instance
                // of ChatMessage to the Firebase database
                FirebaseDatabase.getInstance()
                        .getReference()
                        .push()
                        .setValue(new ChatMessage(input.getText().toString(),
                                FirebaseAuth.getInstance()
                                        .getCurrentUser()
                                        .getEmail())
                        );
                input.setText("");

And this is the method for viewing.

private void displayChatMessages() {
        ListView listOfMessages = (ListView)findViewById(R.id.list_of_messages);
        FirebaseListOptions<ChatMessage> options = new FirebaseListOptions.Builder<ChatMessage>()
                .setQuery(query, ChatMessage.class)
                .build();

        adapter = new FirebaseListAdapter<ChatMessage>(options) {
            @Override
            protected void populateView(View v, ChatMessage model, int position) {
                // Get references to the views of message.xml
                TextView messageText = (TextView)v.findViewById(R.id.message_text);
                TextView messageUser = (TextView)v.findViewById(R.id.message_user);
                TextView messageTime = (TextView)v.findViewById(R.id.message_time);

                // Set their text
                messageText.setText(model.getMessageText());
                messageUser.setText(model.getMessageUser());

                // Format the date before showing it
                messageTime.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)",
                        model.getMessageTime()));
            }
        };

        listOfMessages.setAdapter(adapter);
    }