Issue #2358603 by Berdir: ViewsAjaxController results in fatal error for empty optional arguments

core/modules/views/src/Controller/ViewAjaxController.php

@@ -79,6 +79,13 @@ public function ajaxView(Request $request) {
     if (isset($name) && isset($display_id)) {
       $args = $request->request->get('view_args');
       $args = isset($args) && $args !== '' ? explode('/', $args) : array();
+
+      // Arguments can be empty, make sure they are passed on as NULL so that
+      // argument validation is not triggered.
+      $args = array_map(function ($arg) {
+        return ($arg == '' ? NULL : $arg);
+      }, $args);
+
       $path = $request->request->get('view_path');
       $dom_id = $request->request->get('view_dom_id');
       $dom_id = isset($dom_id) ? preg_replace('/[^a-zA-Z0-9_-]+/', '-', $dom_id) : NULL;
@@ -130,8 +137,9 @@ public function ajaxView(Request $request) {
         // Reuse the same DOM id so it matches that in drupalSettings.
         $view->dom_id = $dom_id;
 
-        $preview = $view->preview($display_id, $args);
-        $response->addCommand(new ReplaceCommand(".view-dom-id-$dom_id", $this->drupalRender($preview)));
+        if ($preview = $view->preview($display_id, $args)) {
+          $response->addCommand(new ReplaceCommand(".view-dom-id-$dom_id", $this->drupalRender($preview)));
+        }
         return $response;
       }
       else {

core/modules/views/tests/src/Unit/Controller/ViewAjaxControllerTest.php

@@ -166,6 +166,27 @@ public function testAjaxViewWithArguments() {
     $this->assertViewResultCommand($response);
   }
 
+  /**
+   * Tests a valid view with arguments.
+   */
+  public function testAjaxViewWithEmptyArguments() {
+    $request = new Request();
+    $request->request->set('view_name', 'test_view');
+    $request->request->set('view_display_id', 'page_1');
+    // Simulate a request that has a second, empty argument.
+    $request->request->set('view_args', 'arg1/');
+
+    list($view, $executable) = $this->setupValidMocks();
+    $executable->expects($this->once())
+      ->method('preview')
+      ->with('page_1', $this->identicalTo(array('arg1', NULL)));
+
+    $response = $this->viewAjaxController->ajaxView($request);
+    $this->assertTrue($response instanceof ViewAjaxResponse);
+
+    $this->assertViewResultCommand($response);
+  }
+
   /**
    * Tests a valid view with a pager.
    */