Using validated method with array in Laravel

This is the rquest body:

{
    "arr": [
        {
            "a": 3,
            "b": 3
        },
        {
            "a": 3,
            "b": 3
        }
    ]
}

and with this validations rules:

    public function rules()
    {
        return [
            // 'arr' => 'array',
            'd.*.a' => 'required'
        ];
    }

The result of dd($request->validated()); is what I want, I don't need b to be included

"arr" => array:2 [
    0 => array:1 [
      "a" => 3
    ]
    1 => array:1 [
      "a" => 3
    ]
  ]

But when I want to validate the array itself like this:

    public function rules()
    {
        return [
            'arr' => 'array',
            'd.*.a' => 'required'
        ];
    }

b will be added to the output

"arr" => array:2 [
    0 => array:1 [
      "a" => 3,
      "b" => 3
    ]
    1 => array:1 [
      "a" => 3,
      "b" => 3
    ]
  ]

How can I prevent adding b to the dd($request->validated()); while validating the array itself?

via Chebli Mohamed