into to java assignment - convert RGB to CMYK JAVA

Question

I had to write a program to convert RGB to CMYK. When I tried running the program I received a java.lang.NullPointerException error. After using a debugger it showed me it had to do with when I called the PrintRGB(RGB) method in the main. I am new to coding and am unsure how to fix this. I googled it and across a few answers but didn't make sense to me since this is my first time coding. Please help me understand this error so I can fix my code. Thank you.

    //Reads the data from the file , populates RGB and converts the colors to CMYK.
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(new File("colors.txt"));
        PrintStream ps = new PrintStream("ArrayResults.txt");
        int[] RGB = new int[3];
        double[] CMYK = new double[4];



            while (sc.hasNextInt()) {
                RGB[0] = sc.nextInt();
                RGB[1] = sc.nextInt();
                RGB[2] = sc.nextInt();

                if (validateRGB(RGB)) {
                    RGBtoCMYK(RGB,CMYK);
                    printRGB(RGB);
                    printCMYK(CMYK);
                } 
                else{
                    ps.println("invalid numbers");
                }

            }

    }

    //Receives the array RGB and determines whether the values are valid.
    public static boolean validateRGB(int[] RGB) throws Exception {
        Scanner sc = new Scanner(new File("colors.txt"));

        for (int i = 0; i < 3; i++) {
            if (RGB[i] >= 0 && RGB[i] <= 255) {
                return true;
            }
        }
        return false;

    }

    //Returns the maximum value in array x which is used to determine white.
    public static int maximum(int x[]) {
        int maximum, i;

        maximum = x[0];
        for (i = 1; i < 3; i++) {
            if (x[i] > maximum) {
                maximum = x[i];
            }
        }
        return maximum;
    }

    //Receives array RGB and places the converted values into array CMYK.
    public static void RGBtoCMYK(int RGB[], double CMYK[]) throws Exception {
        double w;

        w = Math.abs(maximum(RGB) / 255.0);
        CMYK[0] = (w - (RGB[0] / 255.0)) / w;
        CMYK[1] = (w - (RGB[1] / 255.0)) / w;
        CMYK[2] = (w - (RGB[2] / 255.0)) / w;
        CMYK[3] = 1.0 - w;

    }

    //Receives array RGB and prints the values in the array.
    public static void printRGB(int RGB[]) throws Exception {

        for (int i = 0; i < 3; i++) {
            ps.println(RGB[i]);
        }
    }

    //Receives array CMYK and prints the values in the array.
    public static void printCMYK(double CMYK[]) throws Exception {

        for (int i = 0; i < 4; i++) {
            ps.println(CMYK[i]);
        }

    }

}