Allow attribution on orders with no product items. (#160)

Author: rawdreeg

includes/Generator/OrderAttribution.php

@@ -31,15 +31,11 @@ public static function add_order_attribution_meta( $order, $assoc_args = array()
 
 		$order_products = $order->get_items();
 
-		if ( empty( $order_products ) ) {
-			return;
-		}
-
 		$device_type = self::get_random_device_type();
 		$source      = 'woo.com';
 		$source_type = self::get_source_type();
 		$origin      = self::get_origin( $source_type, $source );
-		$product_url = get_permalink( $order_products[ array_rand( $order_products ) ]->get_id() );
+		$product_url = empty( $order_products ) ? '' : get_permalink( $order_products[ array_rand( $order_products ) ]->get_id() );
 		$utm_content = array( '/', 'campaign_a', 'campaign_b' );
 		$utm_content = $utm_content[ array_rand( $utm_content ) ];