I need to add two polynomials, which is composed of two ints. For example, the coefficient and the exponent 3x^2 would be constructed using 3 and 2 as parameters. I am getting a NullPointerException but I can't figure out why. Any help would be appreciated!

public class Polynomial {

private Node poly;

public Polynomial() {
}

private Polynomial(Node p) {
    poly = p;
}

private class Term {

    int coefficient;
    int exponent;

    private Term(int coefficient, int exponent) {
        this.coefficient = coefficient;
        this.exponent = exponent;
    }
}

private class Node {

    private Term data;
    private Node next;

    private Node(Term data, Node next) {
        this.data = data;
        this.next = next;
    }
}

public void addTerm(int coeff, int exp) {
    Node pointer = poly;
    if (pointer.next == null) {
        poly.next = new Node(new Term(coeff, exp), null);
    } else {
        while (pointer.next != null) {
            if (pointer.next.data.exponent < exp) {
                Node temp = new Node(new Term(coeff, exp), pointer.next.next);
                pointer.next = temp;
                return;
            }

            pointer = pointer.next;
        }
        pointer.next = new Node(new Term(coeff, exp), null);
    }

}

public Polynomial polyAdd(Polynomial p) {
    return new Polynomial(polyAdd(this.poly, p.poly));

}

private Node polyAdd(Node p1, Node p2) {
    if (p1 == p2) {
        Term adding = new Term(p1.data.coefficient + p2.data.coefficient,
                p1.data.exponent);
        p1 = p1.next;
        p2 = p2.next;
        return new Node(adding, null);
    }
    if (p1.data.exponent > p2.data.exponent) {
        p2 = p2.next;

    }
    if (p1.data.exponent < p2.data.exponent) {
        p1 = p1.next;

    }
    if (p1.next != null && p2.next != null) {
        return polyAdd(p1, p2);


    }
    return new Node(null, null);
}
}