prepareForValidation(): coercing to array

I handle single or multiple file uploads in my api. In my request class, i want to coerce an instance of \Illuminate\Http\UploadedFile to an array if the client request sends only a single file. The issue is the validation can't catch it if it's not an array.

    public function rules(): array
    {
        return [
            'employee_id' => ['required', 'exists:employees,id'],
            'attachments.*' =>['required', 'file', 'mimes:pdf', 'max:10240'],
        ];
    }

So i was trying to do is smth like this:

    protected function prepareForValidation(): void
    {
        if (! is_array($this->file('attachments'))) {
            $this->merge(['attachments' => $this->array('attachments')]);
        }
    }

Played around it many times and it still won't work. I want to force a file into an array so that i don't have to check it again in my controller once i retrieved the validated data $request->validated().

For now, i have to settle to this:

    public function rules(): array
    {
        $attachmentValidations = ['required', 'file', 'mimes:pdf', 'max:10240'];

        $attachmentRules = is_array($this->file('attachments'))
            ? ['attachments.*' => $attachmentValidations]
            : ['attachments' => $attachmentValidations];

        return array_merge($attachmentRules, [
            'employee_id' => ['required', 'exists:employees,id'],
        ]);
    }

Help plsssssssss