[Demonstration 1]

[Buggy Method]
public void deleteMessage(final int messageIndex) {
    FirebaseDatabase.getInstance().getReference("conversations").child(token).child("messages").child(String.valueOf(messageIndex)).removeValue(new DatabaseReference.CompletionListener() {

        @Override
        public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
            if (databaseError.equals(null)) {
                ll.removeViewAt(messageIndex);
            } else {
                FirebaseErrorHandler.handleError(FirebaseErrorHandler.FIREBASE_ERROR_CODE.DATABASE_ERROR, DoctorConversationActivity.this, new FirebaseException(databaseError.getMessage()));
            }
        }
    });
}

[Buggy Hunk]
if (databaseError.equals(null)) {

[Patch]
if (databaseError == null) {

[Demonstration 2]

[Buggy Method]
public HashMap<Integer, Integer> getHeartbeat() {
    return heartbeat;
}

[Buggy Hunk]
public HashMap<Integer, Integer> getHeartbeat() {

[Patch]
public HashMap<String , Integer> getHeartbeat() {

[Demonstration 3]

[Buggy Method]
private void replyCustomer(String userId, String replyToken, String text) {
    log.info("replyCustomer: userId={}, replyToken={}, text={}", userId, replyToken, text);
    BotInput input = parseCustomerInput(text);
    Conversation conversation = userService.get(userId);
    conversation.addInput(input);
    fsm.handleUserInput(conversation);
    BotActionResponse response = conversation.getLastResponse();
    this.reply(replyToken, renderClient.renderMessage(response));
}

[Buggy Hunk]
Conversation conversation = userService.get(userId);

[Patch]
Conversation conversation = userService.getOrCreate(userId);