diff --git a/core/modules/rest/src/RequestHandler.php b/core/modules/rest/src/RequestHandler.php
index d96df4d..b372a62 100644
--- a/core/modules/rest/src/RequestHandler.php
+++ b/core/modules/rest/src/RequestHandler.php
@@ -105,29 +105,27 @@ public function handle(RouteMatchInterface $route_match, Request $request) {
     // Serialize the outgoing data for the response, if available.
     if ($response instanceof ResourceResponse) {
       $data = $response->getResponseData();
-      if (!is_scalar($data)) {
-        // Serialization can invoke rendering (e.g., generating URLs), but the
-        // serialization API does not provide a mechanism to collect the
-        // bubbleable metadata associated with that (e.g., language and other
-        // contexts), so instead, allow those to "leak" and collect them here in
-        // a render context.
-        // @todo Add test coverage for language negotiation contexts in
-        //   https://www.drupal.org/node/2135829.
-        $context = new RenderContext();
-        $output = $this->container->get('renderer')
-          ->executeInRenderContext($context, function () use ($serializer, $data, $format) {
-            return $serializer->serialize($data, $format);
-          });
-        $response->setContent($output);
-        if (!$context->isEmpty()) {
-          $response->addCacheableDependency($context->pop());
-        }
-
-        $response->headers->set('Content-Type', $request->getMimeType($format));
-        // Add rest settings config's cache tags.
-        $response->addCacheableDependency($this->container->get('config.factory')
-          ->get('rest.settings'));
+      // Serialization can invoke rendering (e.g., generating URLs), but the
+      // serialization API does not provide a mechanism to collect the
+      // bubbleable metadata associated with that (e.g., language and other
+      // contexts), so instead, allow those to "leak" and collect them here in
+      // a render context.
+      // @todo Add test coverage for language negotiation contexts in
+      //   https://www.drupal.org/node/2135829.
+      $context = new RenderContext();
+      $output = $this->container->get('renderer')
+        ->executeInRenderContext($context, function () use ($serializer, $data, $format) {
+          return $serializer->serialize($data, $format);
+        });
+      $response->setContent($output);
+      if (!$context->isEmpty()) {
+        $response->addCacheableDependency($context->pop());
       }
+
+      $response->headers->set('Content-Type', $request->getMimeType($format));
+      // Add rest settings config's cache tags.
+      $response->addCacheableDependency($this->container->get('config.factory')
+        ->get('rest.settings'));
     }
     return $response;
   }
diff --git a/core/modules/rest/tests/src/Kernel/RequestHandlerTest.php b/core/modules/rest/tests/src/Kernel/RequestHandlerTest.php
index c0352cf..969804f 100644
--- a/core/modules/rest/tests/src/Kernel/RequestHandlerTest.php
+++ b/core/modules/rest/tests/src/Kernel/RequestHandlerTest.php
@@ -37,9 +37,6 @@ class RequestHandlerTest extends KernelTestBase {
    */
   public function setUp() {
     parent::setUp();
-//    /** @var \Drupal\rest\Plugin\Type\ResourcePluginManager $plugin_manager */
-//    $plugin_manager = $this->container->get('plugin.manager.rest');
-
     $this->requestHandler = new RequestHandler();
     $this->requestHandler->setContainer($this->container);
   }
@@ -50,22 +47,21 @@ public function setUp() {
    * @covers ::handle
    */
   public function testBaseHandler() {
-
     $request = new Request();
-    $route_match = new RouteMatch('test', new Route('/rest/test', ['_plugin' => 'restplugin']));
+    $route_match = new RouteMatch('test', new Route('/rest/test', ['_plugin' => 'restplugin', '_format' => 'json']));
 
     $resource = $this->prophesize(StubRequestHandlerResourcePlugin::class);
-    // Assert get plugin method is called.
     $resource->get(NULL, $request)
       ->shouldBeCalled();
 
-    // Setup stubbed out plugin manager that will return our plugin.
+    // Setup stub plugin manager that will return our plugin.
     $stub = $this->prophesize(ResourcePluginManager::class);
     $stub->getInstance(['id' => 'restplugin'])
       ->willReturn($resource->reveal());
     $this->container->set('plugin.manager.rest', $stub->reveal());
 
-    // Response returns null this time.
+    // Response returns NULL this time because response from plugin is not
+    // a ResourceResponse so it is passed through directory.
     $response = $this->requestHandler->handle($route_match, $request);
     $this->assertEquals(NULL, $response);
 
@@ -89,51 +85,44 @@ public function testBaseHandler() {
   /**
    * Test that given structured data, the request handler will serialize it.
    *
+   * @dataProvider providerTestSerialization
    * @covers ::handle
    */
-  public function testSerialization() {
+  public function testSerialization($data) {
     $request = new Request();
-    $route_match = new RouteMatch('test', new Route('/rest/test', ['_plugin' => 'restplugin']));
+    $route_match = new RouteMatch('test', new Route('/rest/test', ['_plugin' => 'restplugin', '_format' => 'json']));
 
     $resource = $this->prophesize(StubRequestHandlerResourcePlugin::class);
 
-    // Setup stubbed out plugin manager that will return our plugin.
+    // Setup stub plugin manager that will return our plugin.
     $stub = $this->prophesize(ResourcePluginManager::class);
     $stub->getInstance(['id' => 'restplugin'])
       ->willReturn($resource->reveal());
     $this->container->set('plugin.manager.rest', $stub->reveal());
 
-    $response = new ResourceResponse(['test']);
+    $response = new ResourceResponse($data);
     $resource->get(NULL, $request)
       ->willReturn($response);
     $handler_response = $this->requestHandler->handle($route_match, $request);
     // Content is a serialized version of the data we provided.
-    $this->assertEquals(json_encode(['test']), $handler_response->getContent());
+    $this->assertEquals(json_encode($data), $handler_response->getContent());
   }
 
-  /**
-   * Test that we can serialize an empty dataset.
-   *
-   * @covers ::handle
-   */
-  public function testEmptySerialization() {
-    $request = new Request();
-    $route_match = new RouteMatch('test', new Route('/rest/test', ['_plugin' => 'restplugin']));
-
-    $resource = $this->prophesize(StubRequestHandlerResourcePlugin::class);
-
-    // Setup stubbed out plugin manager that will return our plugin.
-    $stub = $this->prophesize(ResourcePluginManager::class);
-    $stub->getInstance(['id' => 'restplugin'])
-      ->willReturn($resource->reveal());
-    $this->container->set('plugin.manager.rest', $stub->reveal());
-
-    $response = new ResourceResponse([]);
-    $resource->get(NULL, $request)
-      ->willReturn($response);
-    $handler_response = $this->requestHandler->handle($route_match, $request);
-    // Content is a serialized version of the data we provided.
-    $this->assertEquals(json_encode([]), $handler_response->getContent());
+  public function providerTestSerialization() {
+    return [
+      [NULL],
+      [''],
+      ['string'],
+      ['Complex \ string $%^&@ with unicode ΑΒΓΔΕΖΗΘΙΚΛΜΝΞΟΣὨ'],
+      [[]],
+      [['test']],
+      [['test' => 'foobar']],
+      [TRUE],
+      [FALSE],
+      // TODO Not supported. https://www.drupal.org/node/2427811
+      // [new \stdClass()],
+      // [(object) ['test' => 'foobar']],
+    ];
   }
 
 }