Project Euler - #4 - Java - Trying to fine tune, issue with ArrayLists

Question

I've recently written a program to solve problem 4 of Project Euler, I managed to get the answer correct by just searching the list of palindromes for the largest palindrome product.

Now I'm trying to fine tune my program to actually search for the highest palindrome and print it out. Though I keep getting a 'null pointer exception' when trying to add the palindromes to an ArrayList, I have tried an ArrayList and also an ArrayList and both are giving the same exception.

Here is the program, the issue is with the line after:

if (this.isPalindrome(toTest)) { ...

Where I am adding to the array, I don't know what's wrong some help would be greatly appreciated! Thanks in advance.

public void PalinProduct() {
    int pos = 0;
    for (int i = 100; i < 1000; i++) {
        for (int j = 100; j < 1000; j++) {

            int x = (i * j);
            String toTest = Integer.toString(x);
            if (this.isPalindrome(toTest)) {
                palinArray2.add(toTest);
            }

        }
    }
    for (int i = 0; i < palinArray2.size(); i++) {
        int max = 0;
        if (Integer.parseInt(palinArray2.get(i)) > max) {
            pos = i;
        }
    }

    System.out.println("Largest palindrome is " + palinArray2.get(pos));
}