Valores nulos

Minhas classes (todas estão em inglês):

package br.com.alura.threads.mylist;

public class MyListMain {

    public static void main(String[] args) throws InterruptedException {
        final MyList myList = new MyList();

        for (int i = 0; i < 10; i++) {
            new Thread(new AddElementTask(myList, i)).start();
        }

        new Thread(new PrintTask(myList)).start();
    }

}

package br.com.alura.threads.mylist;

public class MyList {

    private final String[] elements = new String[1000];
    private int index = 0;

    public int size() {
        return this.elements.length;
    }

    public synchronized void addElement(final String element) {
        this.elements[index] = element;
        this.index++;

        try {
            Thread.sleep(10);
        } catch (final InterruptedException e) {
            e.printStackTrace();
        }

        if (index == element.length()) {
            System.out.println("List is full, notifying...");
            this.notify();
        }
    }

    public String getElement(int index) {
        return this.elements[index];
    }

}

package br.com.alura.threads.mylist;

public class AddElementTask implements Runnable {

    private final MyList list;
    private final int threadNumber;

    public AddElementTask(final MyList list, final int threadNumber) {
        this.list = list;
        this.threadNumber = threadNumber;
    }

    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            list.addElement("Thread " + threadNumber + " - " + i);
        }
    }

}

package br.com.alura.threads.mylist;

public class PrintTask implements Runnable {

    private final MyList myList;

    public PrintTask(final MyList myList) {
        this.myList = myList;
    }

    @Override
    public void run() {
        synchronized (myList) {
            try {
                System.out.println("Going to sleep, waiting notification...");
                myList.wait();
            } catch (final InterruptedException e) {
                e.printStackTrace();
            }

            for (int i = 0; i < myList.size(); i++) {
                System.out.println(i + " - " + myList.getElement(i));
            }
        }
    }

}

Já encontrei o erro na *MyList.