public function get_attendees_by_order_id( $order_id ) {
			$ticket_id = null;

			// Support an optional second argument while not causing warnings from other ticket provider classes.
			if ( 1 < func_num_args() ) {
				$ticket_id = func_get_arg( 1 );
			}

			/** @var Tribe__Tickets__Attendee_Repository $repository */
			$repository = tribe_attendees( $this->orm_provider );

			$repository->by( 'order', $order_id );

			if ( $ticket_id ) {
				$repository->by( 'ticket', $ticket_id );
			}

			return $this->get_attendees_from_module( $repository->all() );
		}