diff --git a/src/Client.php b/src/Client.php
index 850fcc96..f28e3860 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -1111,8 +1111,8 @@ public function __call($name, $arguments)
         $result = $soapClient->__soapCall(
             $name,
             $this->_preProcessArguments($arguments),
-            null, /* Options are already set to the SOAP client object */
-            (count($soapHeaders) > 0)? $soapHeaders : null,
+            [], /* Options are already set to the SOAP client object */
+            (count($soapHeaders) > 0)? $soapHeaders : [],
             $this->soapOutputHeaders
         );