[Demonstration 1]

[Buggy Method]
public void sendLineToAll(String line, final SendListener listener) {
    for (final BluetoothDevice device : mConnections.keySet()) {
        mConnections.get(device).writeLine(line);
        if (mOnLoseConnectionListener != null) {
            mHandler.post(new Runnable() {

                @Override
                public void run() {
                    listener.onSucceed(device);
                }
            });
        }
    }
}

[Buggy Hunk]
if (mOnLoseConnectionListener != null) {

[Patch]
if (listener != null) {

[Demonstration 2]

[Buggy Method]
public static void invalidateCache() {
    permissionsResults.clear();
}

[Buggy Hunk]
public static void invalidateCache() {

[Patch]
public static synchronized void invalidateCache() {

[Demonstration 3]

[Buggy Method]
public <T> Observable<T> register(Class<T> clazz) {
    String tag = clazz.getName();
    List<Subject> subjectList = subjectMapper.get(tag);
    if (Preconditions.isBlank(subjectList)) {
        subjectList = new ArrayList<>();
        subjectMapper.put(tag, subjectList);
    }
    Subject<T> subject = PublishSubject.create();
    subjectList.add(subject);
    return subject;
}

[Buggy Hunk]
Subject<T> subject = PublishSubject.create();

[Patch]
Subject<T> subject = PublishSubject.<T>create().toSerialized();