Thread.dispatchUncaughtException calls getUncaughtExceptionHandler() which reads volatile field twice:

    private volatile UncaughtExceptionHandler uncaughtExceptionHandler;

    public UncaughtExceptionHandler getUncaughtExceptionHandler() {
        return uncaughtExceptionHandler != null ?
            uncaughtExceptionHandler : group;
    }

    private void dispatchUncaughtException(Throwable e) {
        getUncaughtExceptionHandler().uncaughtException(this, e);
    }

Another thread could change uncaughtExceptionHandler between 2 volatile reads. It will result in NullPointerException