Fix countable error in PHP 7.2; thanks to @andreybolonin in #969

Author: SammyK

.travis.yml

@@ -6,6 +6,7 @@ php:
   - 5.6
   - 7.0
   - 7.1
+  - 7.2
 
 sudo: false
 

src/Facebook/FacebookBatchRequest.php

@@ -39,7 +39,7 @@ class FacebookBatchRequest extends FacebookRequest implements IteratorAggregate,
     /**
      * @var array An array of FacebookRequest entities to send.
      */
-    protected $requests;
+    protected $requests = [];
 
     /**
      * @var array An array of files to upload.