How to allow emty value for Laravel numeric validation

How to set not require numeric validation for Laravel5.2? I just used this Code but when i don't send value or select box haven't selected item I have error the val field most be numeric... I need if request hasn't bed input leave bed alone. leave bed validate ...

$this->validate($request, [
        'provinces_id' => 'required|numeric',
        'type' => 'required',
        'bed' => 'numeric',
]);

via Chebli Mohamed