Laravel 5.1 HttpException in AuthorizesRequests.php line 94

I have the following authorization defined in my controller:

$this->authorize('store', $cart);

In my store method on my cart policy I have the following statement:

public function store(User $user, Cart $cart)
{
    // Check if cart is owned by user 
    if ($user->id != $cart->user_id ) {
       dd($cart);
       return response()->view('errors.404');
    }

    // Some other checks

    return true
}

But I get the following error: HttpException in AuthorizesRequests.php line 94

The error appears to be thrown when trying to evaluate the if statement because when I change comparison operator to == no error is thrown. I've determined this by using dd().

// Check if cart is owned by user
 if ($user->id == $cart->user_id ) {
    dd($cart);  
    return response()->view('errors.404');
 }

Any one have any ideas why this unusual behavior

via Chebli Mohamed