The ControlList constructor takes a validator pointer that can be null. Set its default value to nullptr to simplify code in users of ControlList. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org> Tested-by: Niklas Söderlund <niklas.soderlund@ragnatech.se> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>