Laravel Validator从数组中删除空字段

Question

I'm writing a test case to simulate a creation of a product. When creating the product, I'm passing an array of formats, and for some reasons, when validating with the controller, the thumbnail key is missing from the data.

This is the data I'm sending:

"formats" => array:1 [
  0 => array:3 [
    "upc" => "584979099857"
    "vcode" => "VX43V14FN910479274209"
    "thumbnail" => null
  ]
]

And I send it like the following in my test case:

$response = $this->post(route('products.store'), $product);

For some reasons, when sending the request, the thumbnail => null disappears from the formats attribute.

Therefore, when validating the request, I always get the error that the thumbnail has to be present.

request()->validate([
    'formats' => 'bail|required|array',
    'formats.*.upc' => 'bail|required|string|max:255',
    'formats.*.vcode' => 'bail|required|string|max:255',
    'formats.*.thumbnail' => 'bail|present|image'
]);

I've also tried changing the rules of thumbnail to:

bail|required|nullable|image

Or

bail|nullable|required|image

But then I get the required error.

Does anyone know why the thumbnail key is getting removed from the formats array upon sending the request?