Ensure injectTranslator returns early if no parent container found

Adds a test for a condition reported by @webimpress, detailing expected
behavior if the plugin manager does not have a parent locator when
`injectTranslator()` is called (should return null, not error), and adds
a conditional into `injectTranslator()` to return early if no container
is available.

Author: weierophinney

src/HelperPluginManager.php

@@ -273,16 +273,18 @@ public function getRenderer()
     /**
      * Inject a helper instance with the registered renderer
      *
-     * @param $first
-     * @param $second
+     * @param ContainerInterface|Helper\HelperInterface $first helper instance
+     *     under zend-servicemanager v2, ContainerInterface under v3.
+     * @param ContainerInterface|Helper\HelperInterface $second
+     *     ContainerInterface under zend-servicemanager v3, helper instance
+     *     under v2. Ignored regardless.
      */
     public function injectRenderer($first, $second)
     {
-        if ($first instanceof ContainerInterface) {
-            $helper = $second;
-        } else {
-            $helper = $first;
-        }
+        $helper = ($first instanceof ContainerInterface)
+            ? $second
+            : $first;
+
         $renderer = $this->getRenderer();
         if (null === $renderer) {
             return;
@@ -293,22 +295,35 @@ public function injectRenderer($first, $second)
     /**
      * Inject a helper instance with the registered translator
      *
-     * @param $first
-     * @param $second
+     * @param ContainerInterface|Helper\HelperInterface $first helper instance
+     *     under zend-servicemanager v2, ContainerInterface under v3.
+     * @param ContainerInterface|Helper\HelperInterface $second
+     *     ContainerInterface under zend-servicemanager v3, helper instance
+     *     under v2. Ignored regardless.
      */
     public function injectTranslator($first, $second)
     {
         if ($first instanceof ContainerInterface) {
+            // v3 usage
             $container = $first;
             $helper = $second;
         } else {
+            // v2 usage; grab the parent container
             $container = $second->getServiceLocator();
             $helper = $first;
         }
+
         if (! $helper instanceof TranslatorAwareInterface) {
             return;
         }
 
+        if (! $container) {
+            // Under zend-navigation v2.5, the navigation PluginManager is
+            // always lazy-loaded, which means it never has a parent
+            // container.
+            return;
+        }
+
         if ($container->has('MvcTranslator')) {
             $helper->setTranslator($container->get('MvcTranslator'));
             return;

test/HelperPluginManagerTest.php

@@ -16,6 +16,7 @@
 use Zend\ServiceManager\ServiceManager;
 use Zend\View\Exception\InvalidHelperException;
 use Zend\View\HelperPluginManager;
+use Zend\View\Helper\HeadTitle;
 use Zend\View\Helper\HelperInterface;
 use Zend\View\Helper\Url;
 use Zend\View\Renderer\PhpRenderer;
@@ -175,6 +176,17 @@ public function testIfHelperIsTranslatorAwareAndBothMvcTranslatorAndTranslatorAr
         $this->assertSame($translator, $helper->getTranslator());
     }
 
+    /**
+     * @group 47
+     */
+    public function testInjectTranslatorWillReturnEarlyIfThePluginManagerDoesNotHaveAParentContainer()
+    {
+        $helpers = new HelperPluginManager();
+        $helper = new HeadTitle();
+        $this->assertNull($helpers->injectTranslator($helper, $helpers));
+        $this->assertNull($helper->getTranslator());
+    }
+
     public function testCanOverrideAFactoryViaConfigurationPassedToConstructor()
     {
         $helper  = $this->prophesize(HelperInterface::class)->reveal();