Body should default to null for GET requests with Http Client

src/Http/Client.php

@@ -200,7 +200,7 @@ class Client
     public function get($url, $data = [], array $options = [])
     {
         $options = $this->_mergeOptions($options);
-        $body = [];
+        $body = null;
         if (isset($data['_content'])) {
             $body = $data['_content'];
             unset($data['_content']);