Laravel required_unless validation

I have an problem using required_unless validation.

What I want to do is say that building name is required when building number is empty or other way round so building number is required when building name is empty. At the moment it requires both.

public function rules(Request $request)
{
    $id = $request->input('entity_id');
    $entity = Entity::with('address')
        ->find($id);
    $validation = $entity->id;
    return [
        'name' => 'required|alpha_special|unique:entities,name,'.$validation.'|min:3|max:30',
        'type' => 'required',
        'email' => 'required|email|unique:entities,email,'.$validation,
        'building_name' => 'alpha|required_unless:building_number,value',
        'building_number' => 'numeric|required_unless:building_name,value',
        'street' => 'required|alpha_spaces',
        'town' => 'nullable|alpha',
        'city' => 'nullable|alpha',
        'postcode' => 'required|max:8',
        'telephone' => 'required|telephone',
        'ical' => 'nullable|active_url',
    ];
}

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