Rule::in not working when you have a null value

I have been browsing and I found out that I could filter vlues beeing present in array x. I'm using the Rule::into implode the array as the documentation suggests. I'm trying to use it to filter a pagination (I don't know if this is the correct method of doing it).

Search controller

$validator = Validator::make($request->all(), [
            'profissao'     => 'required|present|max:50|string|Alpha',
            'distrito'      => 'required|max:50|string|Alpha',
            'orderBy'       => [
                'present', // It may not be present since the user may not filter any value
                'nullable', // If the value is not present then it's going to be null
                Rule::in(['preco_hora', 'stars', 'fora_regiao']), 

            ]
        ]);
        if($validator->fails()){
            return redirect('error')->withInput();
        }

But if I try to simplely ask for the results without passing orderBy it throws me to error page. I have made dd($request->oderBy) and it return null as expected. I have tried adding Rule::in(['preco_hora', 'stars', 'fora_regiao', 'null']) but without any lucky.

Any thoughts?