addElements(String e)

    /**
     * Adds e to the list, so the list is still sorted by natural ordering of the
     * elements
     */
    public void addElement(String e) {
            Node newNode = new Node();
            newNode.data = e;
            if (first == null) { // no list -> create list
                first = newNode;
            } else {
                Node prev = null; // previous node
                Node curr = first; // current node
                while (curr != null && curr.data.compareTo(e) < 0) { // NullPointerException on this line
                    prev = curr;
                    curr = curr.next;
                }
                if (curr == null) { // went past end of list, so append
                    prev.next = newNode;
                } else if (curr.data.compareTo(e) == 0) {
                    System.out.println("The element already exists!");
                } else { // between prev and curr, or before start
                    newNode.next = curr;
                    if (prev != null) {
                        prev.next = newNode;
                    } else { // append before start, so 'first' changes
                        first = newNode;
                    }
                }
            }
    }

public void addElement(String e) {
        Node extra = new Node();
        extra.data = e;
        if (first == null) {
            first = extra;
        } else {
            Node prev = null; // the "previous" node
            Node curr = first; // the "current" node
            while (curr != null && curr.data.compareTo(e) < 0) { // NullPointerException on this line
                prev = curr;
                curr = curr.next;
            }
            if (curr == null) {
                prev.next = extra;
            } else if (curr.data.compareTo(e) == 0) {
                System.out.println("Already have a " + e);
            } else {
                extra.next = curr;
                if (prev != null) {
                    prev.next = extra;
                } else {
                    first = extra;
                }
            }
        }
    }

public void addElement(String e) { // only the very first string is ever added by use of this method
        if (first.data == null) {
            first.data = e;
            System.out.println("Success! " + e + " has been added!");
        } else if (first.data.compareTo(e) == 0) {
            System.out.println("The element already exists in the list");
        } else {
            while (first.next != null) {
                if (first.next.data.compareTo(e) != 0) {
                    first.next.data = e;
                } else {
                    first.next = first.next.next;
                }
            }
        }
}