Flutter update is giving me this error: The method '*' was called on null - flutter

Question

I have a flutter app using the flame library. I'm trying to make an object move in a flutter game. When I run the update function, I get the following error:
The method '*' was called on null.
Receiver: null
Tried calling: *(0.0)
Seems like something isn't initialized and the update function is ran before that something is initialized. When I comment out player.update(t) it works, but the update function doesn't get called. What am I doing wrong ad how can I fix it? Here's my code:
Game Controller Class
class GameController extends Game {
Size screenSize;
Player player;
GameController() {
initialize();
}
void initialize() async {
final initDimetion = await Flame.util.initialDimensions();
resize(initDimetion);
player = Player(this);
}
void render(Canvas c) {
Rect bgRect = Rect.fromLTWH(0, 0, screenSize.width, screenSize.height);
Paint bgPaint = Paint()..color = Color(0xFFFAFAFA);
c.drawRect(bgRect, bgPaint);
player.render(c);
}
void update(double t) {
if (player is Player) { // Tried adding this if statement but it didn't work
player.update(t);
}
}
void resize(Size size) {
screenSize = size;
}
}
Player Class
class Player {
final GameController gameController;
Rect playerRect;
double speed;
Player(this.gameController) {
final size = 40.0;
playerRect = Rect.fromLTWH(gameController.screenSize.width / 2 - size / 2,
gameController.screenSize.height / 2 - size / 2, size, size);
}
void render(Canvas c) {
Paint color = Paint()..color = Color(0xFF0000FF);
c.drawRect(playerRect, color);
}
void update(double t) {
double stepDistance = speed * t;
Offset stepToSide = Offset.fromDirection(90, stepDistance);
playerRect = playerRect.shift(stepToSide);
}
}

Answer 1

You never initialize the speed attribute of Player to a value. So speed * t in Player.update causes this error.
Simply initialize the speed attribute in the constructor
Player(this.gameController) {
final size = 40.0;
this.speed = 0;
playerRect = Rect.fromLTWH(gameController.screenSize.width / 2 - size / 2,
gameController.screenSize.height / 2 - size / 2, size, size);
}