Hi everyone I'm very new to processing but had to do my graduation project with it. Below is my code, but when closing minim I get "Null Pointer Exception" error. What can I do and what does it mean?

import processing.serial.*;
import processing.video.*;
import ddf.minim.*;

//BufferedReader input;
PrintWriter output;
AudioPlayer player;
Minim minim;

Capture myCapture;
Movie myMovie;
Serial myPort;  // Create object from Serial class

Boolean videoplaying = false;
Boolean captureon = false;

int val = 11;      // Data received from the serial port

int pir = 1;
int ldr = 1;
int pir_pre = 0;
int ldr_pre = 0;
int t = 0;
int timer = 0;
int imagenum = 1;

void setup()
{
 size(320, 240, P2D);
 background(0);
 minim = new Minim(this);
 
 //myMovie.loop();
 
 myCapture = new Capture(this, width, height, 30);
 
 String portName = Serial.list()[0];
 myPort = new Serial(this, portName, 9600);
 
 // Create a new file in the sketch directory
 output = createWriter("bikbik.txt");
//  input = createReader("bikbik.txt");
 
//  inputRead();
}

void draw()
{
 if ( myPort.available() > 0) {  // If data is available,
   val = myPort.read();         // read it and store it in val
 }
 
 pir = val/10;
 ldr = val%10;
 
 print("pir=");
 print(pir);
 print(" - ldr=");
 println(ldr);
 println(timer);

if(pir == 0)
{
  timer=0;
}

if(ldr == 0){
 timer=1000;
}

if (timer >= 3000) {
 timer=1000;
}

if (timer<1000 && !videoplaying) {
 int rand = int(random(1,4));
 println(rand);
 player = minim.loadFile(""+rand+".mp3", 2048);
 myMovie = new Movie(this, ""+rand+".mov");
 player.cue(0);
 player.play();
 myMovie.play();
 videoplaying = true;
}

else if (timer >=1000 && videoplaying) {
 player.pause();
 myMovie.stop();
 videoplaying=false;
}

if (videoplaying) {
 image(myMovie, 0, 0, width, height);
}

timer++;

if(ldr == 0 && !captureon) {
  t = (millis())%10000;
  captureon = true;
  captureSave();
}
if (ldr == 1) {
  captureon = false;
}
}

void movieEvent(Movie myMovie) {
 myMovie.read();
}

void captureSave()
{
 //rotateImage(myCapture, 180);
 image(rotateImage(myCapture, 180), 0, 0);
 //save(year()+"/"+month()+"/"+day()+"/"+minute()+"redhot.png");
 save("img"+imagenum+".jpg");
 imagenum++;
}

void captureEvent(Capture myCapture) {
 myCapture.read();
}


PImage rotateImage(PImage img, int angle)
{
 PImage rot;
 int numPixels = img.height*img.width;
 if (abs(angle) == 180)
 {
   rot = new PImage(img.width,img.height);
 }
 else
 {
   rot = new PImage(img.height,img.width);
 }
 img.loadPixels();
 
 int rotpx = 0;
 for (int i = 0; i < numPixels; i++)
 {
     int x0 = i % img.width;
     int y0 = floor(i / img.width);
     
     // for each pixel calculates new x & y coordinates and index
     if (angle == 90)
     {
       int x1 = abs(y0 + 1 - img.height);
       int y1 = x0;
       rotpx = x1 + (y1 * rot.width);
     }
     else if (angle == -90 || angle == 270)
     {
       int x1 = y0;
       int y1 = abs(x0 + 1 - img.width);
       rotpx = x1 + (y1 * rot.width);
     }
     else if (angle == 180 || angle == -180)
     {
       // 180 is the easiest, just flip the array index...
       rotpx = numPixels - 1 - i;
     }
     else
     {
       // angles other than 90/180 are far more complicated...
       println("Not implemented, sorry ");
     }
     
     rot.pixels[rotpx] = img.pixels[i];
 }
 rot.updatePixels();
 return rot;
}

void keyPressed() {
 output.println(imagenum);
 output.flush(); // Writes the remaining data to the file
 output.close(); // Finishes the file
 exit(); // Stops the program
}

/*
void inputRead ()
{
 String line1;
 //try {
   line1 = input.readLine();
 //} catch (IOException e) {
 //  e.printStackTrace();
 //  line1 = null;
 //}
 if (line1 == null) {
   // Stop reading because of an error or file is empty
   imagenum = 1;
 //  noLoop();  
 } else {
   String[] pieces = split(line1, TAB);
   int x = int(pieces[0]);
   imagenum = x + 1;
 }
}
*/

void stop()
{
player.close();
 minim.stop();
 super.stop();
}


Here is the error:
Exception in thread "Animation Thread" java.lang.NullPointerException
     at Bike_1_kb5.stop(Bike_1_kb5.java:230)
     at processing.core.PApplet.die(PApplet.java:2535)
     at processing.core.PApplet.die(PApplet.java:2545)
     at processing.video.Capture.init(Capture.java:241)
     at processing.video.Capture.<init>(Capture.java:154)
     at processing.video.Capture.<init>(Capture.java:115)
     at Bike_1_kb5.setup(Bike_1_kb5.java:58)
     at processing.core.PApplet.handleDraw(PApplet.java:1571)
     at processing.core.PApplet.run(PApplet.java:1496)
     at java.lang.Thread.run(Thread.java:613)