null pointer exception

hey guys, i'm new , attempting create simon says program ardruino. arduino program works fine when try communicate serial port processing keep getting "null pointer exception" message. have looked online nothing makes sense in relation specific problem. please me out, appreciate it. here processing code:

code: [select]


void setup() {
  println(serial.list());


}
void draw(){
if (key == 'a'){
  port.write(1);
}
if (key == 'w'){
  port.write(2);
}
if (key == 'd'){
  port.write(3);
}
if (key == 's'){
  port.write(4);
}
}


quote

...when try communicate serial port processing keep getting "null pointer exception" message...

processing raising exception?

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