Undefined offset Error checking php - php

Question

Im getting an undefined offset error. I know why i am getting the error and where it is. What i am trying to work out is how to implement the appropriate error checking to prevent this from happening. The method is currently being called via ajax and thus the error cause's issues with the return of any strings etc.
Following is the class's method being called, its variables are being set vie $_GET.
$id = $_GET['id'];
$product = $_GET['name'];
$price = $_GET['price'];
//check for existing product
for($i = 0; $i <= count($_SESSION['BASKET']); $i++) {
//if product exsits incrent by 1
if($_SESSION['BASKET'][$i]['id'] == $id){
$_SESSION['BASKET'][$i]['amount'] = $_SESSION['BASKET'][$i]['amount'] + 1;
break;
//if doesnt exsist creat product array
} else {
$item = array('id' => $id,'amount' => 1,'product' => $product,'price' => $price);
}
}
if(isset($item)){
//push product to session array
array_push($_SESSION['BASKET'], $item);
}
As you can see the method checks to see if the basket currently contains a product and updates by incrementing the quantity ('amount'). I have a constructer that creates the basket array in the class. The issue occurs when the $_SESSION['BASKET'] is called and is empty but still exists as in :
array (
)
this creates and undefined offset error when checking the id in the if statement as the array technically exists but the offset 0 does not. Any ideas how i can handle this?.
Code changes i a have made that cause the same error
if(isset($_SESSION['BASKET'][$i]) && $_SESSION['BASKET'][$i]['id'] == $id){

Answer 1

I have moved the logic outside the loop and added a bool variable, i can then query this to check if a item was found in the array. This allowed me to create another if statement to check if the sessions values were set rather than checking if the array was created.
$id = $_GET['id'];
$product = $_GET['name'];
$price = $_GET['price'];
$exsist = false;
//check for existing product
for($i = 0; $i <= count($_SESSION['BASKET']); $i++) {
if(isset($_SESSION['BASKET'][$i])){
//if product exsits incrent by 1
if(isset($_SESSION['BASKET'][$i]) && $_SESSION['BASKET'][$i]['id'] == $id){
$_SESSION['BASKET'][$i]['amount'] = $_SESSION['BASKET'][$i]['amount'] + 1;
$exsist = true;
break;
}
}
}
if($exsist != true){
$item = array('id' => $id,'amount' => 1,'product' => $product,'price' => $price);
array_push($_SESSION['BASKET'], $item);
}