Laravel: how to merge new UploadedFile object in Request / FormRequest?

UploadFileRequest.php

<?php

namespace App\Http\Requests\Files;

use App\Helpers\File\FileHelper;
use App\Overrides\FormRequest\FormRequest;

class UploadFileRequest extends FormRequest
{
    public function rules(): array
    {
        return [
            'file' => 'required|file',
        ];
    }

    /**
     * This method prepares file instante
     */
    protected function prepareForValidation()
    {
        // This condition means that file parameter is received, but it is not file.
        // Potentially it is base64 encoded file.
        // Let's get new UploadedFile object from it and then merge it in the request
        if (!$this->file('file') && $this->input('file')) {
            // Create new UploadedFile object from base64 string
            // See the helper here: https://gist.github.com/waska14/8b3bcebfad1f86f7fcd3b82927576e38
            $file = FileHelper::fromBase64($this->input('file'));

            // Add it in files
            $this->files->add(['file' => $file]);

            // Merge it in request also (As I found this is not needed in every case)
            $this->merge(['file' => $file]);

            // Clear convertedFiles array (set null).
            // This action forces $request->file() method to convert request files again
            // So when you use $request->file('file') or $request->allFiles() or something like this, our new 'file'
            // object will be available!
            $this->convertedFiles = null;
        }
    }
}