diff --git a/core/lib/Drupal/Core/DependencyInjection/Container.php b/core/lib/Drupal/Core/DependencyInjection/Container.php
index 3c8b631..aef2323 100644
--- a/core/lib/Drupal/Core/DependencyInjection/Container.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Container.php
@@ -362,7 +362,7 @@ protected function createService(array $definition, $id) {
    * {@inheritdoc}
    */
   public function set($id, $service, $scope = self::SCOPE_CONTAINER) {
-    if (isset($service)) {
+    if (isset($service) && is_object($service)) {
       $service->_serviceId = $id;
     }
     $this->services[$id] = $service;
@@ -456,7 +456,8 @@ protected function resolveServicesAndParameters($arguments) {
           $name = $argument->name;
           if (!isset($this->parameters[$name])) {
             $arguments[$key] = $this->getParameter($name);
-            // This can never be reached as getParameter() throws an Exception.
+            // This can never be reached as getParameter() throws an Exception,
+            // because we already checked that the parameter is not set above.
           }
 
           // Update argument.
diff --git a/core/lib/Drupal/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumper.php b/core/lib/Drupal/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumper.php
index d433375..dcf7227 100644
--- a/core/lib/Drupal/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumper.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumper.php
@@ -369,7 +369,7 @@ protected function dumpCallable($callable) {
   protected function getPrivateServiceCall($id, Definition $definition, $shared = FALSE) {
     $service_definition = $this->getServiceDefinition($definition);
     if (!$id) {
-      $hash = sha1(serialize($service_definition));
+      $hash = hash('sha1', serialize($service_definition));
       $id = 'private__' . $hash;
     }
     return (object) array(
diff --git a/core/lib/Drupal/Core/DependencyInjection/PhpArrayContainer.php b/core/lib/Drupal/Core/DependencyInjection/PhpArrayContainer.php
index 4ca94fa..2de82b0 100644
--- a/core/lib/Drupal/Core/DependencyInjection/PhpArrayContainer.php
+++ b/core/lib/Drupal/Core/DependencyInjection/PhpArrayContainer.php
@@ -247,7 +247,8 @@ protected function resolveServicesAndParameters($arguments) {
         $name = substr($argument, 1, -1);
         if (!isset($this->parameters[$name])) {
           $arguments[$key] = $this->getParameter($name);
-          // This can never be reached as getParameter() throws an Exception.
+          // This can never be reached as getParameter() throws an Exception,
+          // because we already checked that the parameter is not set above.
         }
         $argument = $this->parameters[$name];
         $arguments[$key] = $argument;
@@ -264,7 +265,9 @@ protected function resolveServicesAndParameters($arguments) {
         if (isset($this->services[$id])) {
           $arguments[$key] = $this->services[$id];
         }
-        $arguments[$key] = $this->get($id, $invalid_behavior);
+        else {
+          $arguments[$key] = $this->get($id, $invalid_behavior);
+        }
       }
     }
 
diff --git a/core/modules/system/src/Tests/ServiceProvider/ServiceProviderWebTest.php b/core/modules/system/src/Tests/ServiceProvider/ServiceProviderWebTest.php
index 15120a5..8a6d3bc 100644
--- a/core/modules/system/src/Tests/ServiceProvider/ServiceProviderWebTest.php
+++ b/core/modules/system/src/Tests/ServiceProvider/ServiceProviderWebTest.php
@@ -31,7 +31,7 @@ class ServiceProviderWebTest extends WebTestBase {
    */
   public function testServiceProviderRegistrationIntegration() {
     $this->assertTrue(\Drupal::hasService('service_provider_test_class'), 'The service_provider_test_class service has been registered to the DIC');
-    // The event subscriber method in the test class calls drupal_set_message
+    // The event subscriber method in the test class calls drupal_set_message()
     // with a message saying it has fired. This will fire on every page request
     // so it should show up on the front page.
     $this->drupalGet('');
diff --git a/core/modules/update/src/Tests/UpdateTestBase.php b/core/modules/update/src/Tests/UpdateTestBase.php
index 33ee105..faec496 100644
--- a/core/modules/update/src/Tests/UpdateTestBase.php
+++ b/core/modules/update/src/Tests/UpdateTestBase.php
@@ -35,7 +35,7 @@ protected function setUp() {
 
     // Change the root path which Update Manager uses to install and update
     // projects to be inside the testing site directory. See
-    // \Drupal\updateUpdateRootFactory::get() for equivalent changes to the
+    // \Drupal\update\UpdateRootFactory::get() for equivalent changes to the
     // test child site.
     $request = \Drupal::request();
     $update_root = $this->container->get('update.root') . '/' . DrupalKernel::findSitePath($request);
diff --git a/core/tests/Drupal/Tests/Core/DependencyInjection/ContainerTest.php b/core/tests/Drupal/Tests/Core/DependencyInjection/ContainerTest.php
index ca8cf98..f4d05e9 100644
--- a/core/tests/Drupal/Tests/Core/DependencyInjection/ContainerTest.php
+++ b/core/tests/Drupal/Tests/Core/DependencyInjection/ContainerTest.php
@@ -239,7 +239,7 @@ public function testGetForCircularServices() {
   }
 
   /**
-   * Tests that Container::get() for non-existant services works properly.
+   * Tests that Container::get() for non-existent services works properly.
    *
    * @covers ::get
    * @covers ::createService
@@ -273,7 +273,7 @@ public function testGetForSerializedServiceDefinition() {
   }
 
   /**
-   * Tests that Container::get() for non-existant parameters works properly.
+   * Tests that Container::get() for non-existent parameters works properly.
    *
    * @covers ::get
    * @covers ::createService
@@ -303,7 +303,7 @@ public function testGetForParameterDependencyWithExceptionOnSecondCall() {
   }
 
   /**
-   * Tests that Container::get() for non-existant parameters works properly.
+   * Tests that Container::get() for non-existent parameters works properly.
    *
    * @covers ::get
    * @covers ::createService
@@ -328,7 +328,7 @@ public function testGetForNonExistantServiceDependency() {
   }
 
   /**
-   * Tests that Container::get() for non-existant dependencies works properly.
+   * Tests that Container::get() for non-existent dependencies works properly.
    *
    * @covers ::get
    * @covers ::createService
@@ -342,7 +342,7 @@ public function testGetForNonExistantServiceDependencyWithException() {
   }
 
   /**
-   * Tests that Container::get() for non-existant services works properly.
+   * Tests that Container::get() for non-existent services works properly.
    *
    * @covers ::get
    * @covers ::createService
diff --git a/core/tests/Drupal/Tests/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumperTest.php b/core/tests/Drupal/Tests/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumperTest.php
index 62c9a35..5659108 100644
--- a/core/tests/Drupal/Tests/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumperTest.php
+++ b/core/tests/Drupal/Tests/Core/DependencyInjection/Dumper/OptimizedPhpArrayDumperTest.php
@@ -585,7 +585,7 @@ protected function getParameterCall($name) {
 namespace Symfony\Component\ExpressionLanguage {
   if (!class_exists('\Symfony\Component\ExpressionLanguage\Expression')) {
     /**
-     * Dummy class to ensure non-existant Symfony component can be tested.
+     * Dummy class to ensure non-existent Symfony component can be tested.
      */
     class Expression {