Make sure that the optional dependancies are last in the constructor

Author: dmanners

app/code/Magento/Captcha/Controller/Adminhtml/Refresh/Refresh.php

@@ -21,15 +21,16 @@ class Refresh extends \Magento\Backend\App\Action
     protected $captchaHelper;
 
     /**
+     * Refresh constructor.
      * @param \Magento\Backend\App\Action\Context $context
-     * @param \Magento\Framework\Serialize\SerializerInterface|null $serializer
      * @param \Magento\Captcha\Helper\Data $captchaHelper
+     * @param \Magento\Framework\Serialize\SerializerInterface|null $serializer
      * @throws \RuntimeException
      */
     public function __construct(
         \Magento\Backend\App\Action\Context $context,
-        \Magento\Framework\Serialize\SerializerInterface $serializer = null,
-        \Magento\Captcha\Helper\Data $captchaHelper
+        \Magento\Captcha\Helper\Data $captchaHelper,
+        \Magento\Framework\Serialize\SerializerInterface $serializer = null
     ) {
         parent::__construct($context);
         $this->serializer = $serializer ?: \Magento\Framework\App\ObjectManager::getInstance()

app/code/Magento/Captcha/Model/Customer/Plugin/AjaxLogin.php

@@ -48,8 +48,8 @@ public function __construct(
         CaptchaHelper $helper,
         SessionManagerInterface $sessionManager,
         JsonFactory $resultJsonFactory,
-        \Magento\Framework\Serialize\SerializerInterface $serializer = null,
-        array $formIds
+        array $formIds,
+        \Magento\Framework\Serialize\SerializerInterface $serializer = null
     ) {
         $this->helper = $helper;
         $this->sessionManager = $sessionManager;

app/code/Magento/Captcha/Test/Unit/Model/Customer/Plugin/AjaxLoginTest.php

@@ -96,8 +96,8 @@ protected function setUp()
             $this->captchaHelperMock,
             $this->sessionManagerMock,
             $this->jsonFactoryMock,
-            $this->serializerMock,
-            $this->formIds
+            $this->formIds,
+            $this->serializerMock
         );
     }