Undefined offset: 1 error for laravel validation

I have some validation on my form in laravel to ensure the gift the user is claiming is one assigned to their campaign with the below code

'gift_id' => 'required|int|exists:gifts,campaign_id,' . \Auth::user()->campaign->id,

But on form submission I am getting the following error

ErrorException in ValidatesAttributes.php line 721: Undefined offset: 1

Could someone please help me out?

Thanks

via user6073700