Empty input values in rules() method of FormRequest

Hello everyone!

I have a strange issue. I can't access input parameters in rules method of FormRequest. The following code returns empty array:

public function rules()
    {
        dd($this->all());
        $rules = [
            'name'  => 'required|min:5|max:255|unique:products,name,' . $this->get('id'),
            'sku'   => 'required|max:255|unique:products,sku,' . $this->get('id'),
            'slug'  => 'required|max:255|unique:products,slug,' . $this->get('id'),
            'price' => 'required|numeric',
        ];



        /*foreach ($this->input('variations') as $index => $variation) {
            $rules['variations.' . $index . 'sku'] = 'unique:variations,sku,' . $this->input('productVariationIDs')[$index];
        }

        dd($rules);*/

        return $rules;
    }

However if I try to access the same input inside the other method of the class then I get it without any issue. For example in the authorize method:

public function authorize()
    {dd($this->all());
        // only allow updates if the user is logged in
        return backpack_auth()->check();
    }

I also find out that rules() method is called before authorize(), so I assume that request is not fully instantiated. But this is very strange as after googling I couldn't find anybody with the same issue.

So my question is how can I access input parameters inside the rules() method of class that extends FormRequest class?

This is Laravel 5.7 with installed Backpack.