Arrays in array, 100 rows, dynamic columns

I'm trying to get this:

arrays[1][0] = 5

arrays[2][0] = 7
arrays[2][1] = 2

arrays[3][0] = 6
arrays[3][1] = 9
arrays[3][2] = 11

So I want arrays[1][] to have one element of random data, arrays[2][] to have 2 elements of random data and so on until I have 100 arrays. So my last array would be arrays[100][] with 100 elements of random data.

This is the code I have now but I get a NullPointerException when arrays[i][j] = generator.nextInt(max) is executed:

Comparable[][] arrays = new Comparable[100][];
    for (int i=1; i<101;i++){
        for (int j=0; j <= i-1; j++){
            arrays[i][j] = generator.nextInt(max);
        }
    }