Error #1009, ActionScript 3, Bullet is null - actionscript-3

Question

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Main_fla::MainTimeline/BulletFire()[Main_fla.MainTimeline::frame32:68]. Is occurring and I have no idea why...PLEASE HELP, it has been days of me troubleshooting this and i am completely lost. Thanks, also, for some reason when I fire the bullet it only goes at 45 degrees and 225 degrees...Thanks guys
//Create an array to hold multiple sprites
var mySpriteHolder:Array = [];
//Create a counter to keep track of the number of sprites
var lbCounter:int = 0;
//Maximum number of sprites on the canvas
var maxLB:int = 1;
//Keypress Code
stage.addEventListener(MouseEvent.CLICK, dropBullet);
//Function for the mouse event to fire bullet
function dropBullet(evt:MouseEvent):void{
var bcos:Number = Math.cos((Turret.rotation) * Math.PI / 180);
var bsin:Number = Math.sin((Turret.rotation) * Math.PI / 180);
//starting x and y
var startx:Number = Turret.x + (15 * bcos);
var starty:Number = Turret.y + (15 * bsin);
//calculates where the bullet needs to go by aiming in front of the gun
var endx:Number = Turret.x + (50 * bcos);
var endy:Number = Turret.y + (50 * bsin);
var Bullet:MovieClip = new bullet();
Bullet.x = startx;
Bullet.y = starty;
Bullet.xspeed = (endx - startx)/5;
Bullet.yspeed = (endx - startx)/5;
mySpriteHolder.push(Bullet);
stage.addChild(Bullet);
//this calls the move down function
stage.addEventListener(Event.ENTER_FRAME,BulletFire);
}
//Function to shoot bullet
function BulletFire(evt:Event):void{
var Bullet:MovieClip;
//Use a for loop to move the Bullets
for(var i:int=0; i<=mySpriteHolder.length; i++){
Bullet = mySpriteHolder[i];
//Bounds Collision
if(Bullet.hitTestObject(Up)){
Bullet.yspeed*=-1;
}
if(Bullet.hitTestObject(Lower)){
Bullet.yspeed*=-1;
}
if(Bullet.hitTestObject(Left)){
Bullet.xspeed*=-1;
}
if(Bullet.hitTestObject(Right)){
Bullet.xspeed*=-1;
}
//Blockade Collision
for(var t in myBlockadeHolder){
if(Bullet.hitTestObject(myBlockadeHolder[t])){
trace("test");
}
}
//Target Collision
for(var c in mytargetHolder){
if(Bullet.hitTestObject(mytargetHolder[c])){
stage.removeChild(Bullet);
mySpriteHolder.splice(i,1);
lbCounter --;
mytargetHolder[c].y = Math.random()*390 + 10;
mytargetHolder[c].x = Math.random()*390 + 10;
while(mytargetHolder[c].hitTestObject(Turret)){
mytargetHolder[c].y = Math.random()*390 + 10;
mytargetHolder[c].x = Math.random()*390 + 10;
}
}
for(var a in mytargetHolder){
for(var s in mytargetHolder){
while(mytargetHolder[a].hitTestObject(mytargetHolder[s])&& a!=s){
mytargetHolder[a].y = Math.random()*390 + 10;
mytargetHolder[a].x = Math.random()*390 + 10;
}
}
for(var g in myBlockadeHolder){
while(mytargetHolder[a].hitTestObject(myBlockadeHolder[g])&& a!=g){
mytargetHolder[a].y = Math.random()*390 + 10;
mytargetHolder[a].x = Math.random()*390 + 10;
}
}
}
}
Bullet.y += Bullet.yspeed;
Bullet.x += Bullet.xspeed;
}
}

Answer 1

mySpriteHolder.splice(i,1);
This line is probably causing some unexpected results (and possibly your error) as you're splicing objects from the array your loop is working incrementally from. It's important to understand that when you splice an object in AS3 you're effectively removing that element and all indices that follow move down the splicing amount. Try working backwards in the loop instead:
for(var i:int=mySpriteHolder.length-1; i>=0; i--){
Also, this line should be moved out of your MouseClick Event as you're adding multiple ENTER_FRAME events every time a bullet is placed. As it is right now it's going to do an additional bulletFire() pass every time you mouse click:
stage.addEventListener(Event.ENTER_FRAME,BulletFire);

Answer 2

For a start:
for (var i:int = 0; i < mySpriteHolder.length; i++) {
...
i.e. change <= to <. If i becomes mySpriteHolder.length then you'll get an out-of-bounds exception.
Next:
stage.removeChild(Bullet);
mySpriteHolder.splice(i--, 1);
i.e. when you remove the current element from the array, you also decrement the index i. It'll get incremented again in the next iteration, so you'll be at the same index. For example, if you delete the 5th element, you want to look at the new 5th element (previously the 6th) in the next iteration, as opposed to the new 6th element (previously the 7th). In your current code, you're inadvertently skipping one - not to mention that itself could give you an out-of-bounds exception.
By "out-of-bounds" I mean Bullet being undefined.