Fix handling of possible null return

Author: staabm

src/Framework/MockObject/Generator/Generator.php

@@ -468,7 +468,7 @@ public function generateClassFromWsdl(string $wsdlFile, string $className, array
 
         try {
             $client   = new SoapClient($wsdlFile, $options);
-            $_methods = array_unique($client->__getFunctions());
+            $_methods = array_unique($client->__getFunctions() ?? []);
 
             unset($client);
         } catch (SoapFault $e) {