@Override
    public void uncaughtException(Thread t, Throwable e) {
        if (this.firstException == null)
            this.firstException = e;
    }
An UncaughtExceptionHandler that can be registered with one or more threads which tracks the
first exception so the main thread can check for uncaught exceptions.
connect/runtime/src/test/java/org/apache/kafka/connect/util/TestBackgroundThreadExceptionHandler.java