diff --git a/service_container.rst b/service_container.rst
index ff80ac27a14..09e26cd4d0b 100644
--- a/service_container.rst
+++ b/service_container.rst
@@ -340,7 +340,7 @@ you can type-hint the new ``SiteUpdateManager`` class and use it::
 
     // src/Controller/SiteController.php
     namespace App\Controller;
-    
+
     // ...
     use App\Service\SiteUpdateManager;
 
@@ -378,7 +378,7 @@ example, suppose you want to make the admin email configurable:
     +    private $adminEmail;
 
     -    public function __construct(MessageGenerator $messageGenerator, MailerInterface $mailer)
-    +    public function __construct(MessageGenerator $messageGenerator, MailerInterface $mailer, $adminEmail)
+    +    public function __construct(MessageGenerator $messageGenerator, MailerInterface $mailer, string $adminEmail)
         {
             // ...
     +        $this->adminEmail = $adminEmail;
diff --git a/service_container/autowiring.rst b/service_container/autowiring.rst
index 167fb4562f4..04058c6b9ac 100644
--- a/service_container/autowiring.rst
+++ b/service_container/autowiring.rst
@@ -29,7 +29,7 @@ Start by creating a ROT13 transformer class::
 
     class Rot13Transformer
     {
-        public function transform($value)
+        public function transform(string $value): string
         {
             return str_rot13($value);
         }
@@ -41,6 +41,7 @@ And now a Twitter client using this transformer::
     namespace App\Service;
 
     use App\Util\Rot13Transformer;
+    // ...
 
     class TwitterClient
     {
@@ -51,7 +52,7 @@ And now a Twitter client using this transformer::
             $this->transformer = $transformer;
         }
 
-        public function tweet($user, $key, $status)
+        public function tweet(User $user, string $key, string $status): void
         {
             $transformedStatus = $this->transformer->transform($status);
 
@@ -129,6 +130,8 @@ Now, you can use the ``TwitterClient`` service immediately in a controller::
 
     use App\Service\TwitterClient;
     use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+    use Symfony\Component\HttpFoundation\Request;
+    use Symfony\Component\HttpFoundation\Response;
     use Symfony\Component\Routing\Annotation\Route;
 
     class DefaultController extends AbstractController
@@ -136,7 +139,7 @@ Now, you can use the ``TwitterClient`` service immediately in a controller::
         /**
          * @Route("/tweet", methods={"POST"})
          */
-        public function tweet(TwitterClient $twitterClient)
+        public function tweet(TwitterClient $twitterClient, Request $request): Response
         {
             // fetch $user, $key, $status from the POST'ed data
 
@@ -288,7 +291,7 @@ To follow this best practice, suppose you decide to create a ``TransformerInterf
 
     interface TransformerInterface
     {
-        public function transform($value);
+        public function transform(string $value): string;
     }
 
 Then, you update ``Rot13Transformer`` to implement it::
@@ -388,7 +391,7 @@ Suppose you create a second class - ``UppercaseTransformer`` that implements
 
     class UppercaseTransformer implements TransformerInterface
     {
-        public function transform($value)
+        public function transform(string $value): string
         {
             return strtoupper($value);
         }
@@ -426,7 +429,7 @@ the injection::
             $this->transformer = $shoutyTransformer;
         }
 
-        public function toot($user, $key, $status)
+        public function toot(User $user, string $key, string $status): void
         {
             $transformedStatus = $this->transformer->transform($status);
 
@@ -565,12 +568,12 @@ to inject the ``logger`` service, and decide to use setter-injection::
         /**
          * @required
          */
-        public function setLogger(LoggerInterface $logger)
+        public function setLogger(LoggerInterface $logger): void
         {
             $this->logger = $logger;
         }
 
-        public function transform($value)
+        public function transform(string $value): string
         {
             $this->logger->info('Transforming '.$value);
             // ...
diff --git a/service_container/calls.rst b/service_container/calls.rst
index 00069a2ccb2..78418aadf13 100644
--- a/service_container/calls.rst
+++ b/service_container/calls.rst
@@ -22,7 +22,7 @@ example::
     {
         private $logger;
 
-        public function setLogger(LoggerInterface $logger)
+        public function setLogger(LoggerInterface $logger): void
         {
             $this->logger = $logger;
         }
@@ -97,7 +97,7 @@ instead of mutating the object they were called on::
         /**
          * @return static
          */
-        public function withLogger(LoggerInterface $logger)
+        public function withLogger(LoggerInterface $logger): self
         {
             $new = clone $this;
             $new->logger = $logger;
diff --git a/service_container/compiler_passes.rst b/service_container/compiler_passes.rst
index 4d959e93dc6..79f666a4237 100644
--- a/service_container/compiler_passes.rst
+++ b/service_container/compiler_passes.rst
@@ -52,7 +52,7 @@ and process the services inside the ``process()`` method::
 
         // ...
 
-        public function process(ContainerBuilder $container)
+        public function process(ContainerBuilder $container): void
         {
             // in this method you can manipulate the service container:
             // for example, changing some container service:
@@ -81,7 +81,7 @@ method in the extension)::
 
     class MyBundle extends Bundle
     {
-        public function build(ContainerBuilder $container)
+        public function build(ContainerBuilder $container): void
         {
             parent::build($container);
 
diff --git a/service_container/configurators.rst b/service_container/configurators.rst
index 92c1afc5794..5331d0ba7ac 100644
--- a/service_container/configurators.rst
+++ b/service_container/configurators.rst
@@ -28,7 +28,7 @@ You start defining a ``NewsletterManager`` class like this::
     {
         private $enabledFormatters;
 
-        public function setEnabledFormatters(array $enabledFormatters)
+        public function setEnabledFormatters(array $enabledFormatters): void
         {
             $this->enabledFormatters = $enabledFormatters;
         }
@@ -45,7 +45,7 @@ and also a ``GreetingCardManager`` class::
     {
         private $enabledFormatters;
 
-        public function setEnabledFormatters(array $enabledFormatters)
+        public function setEnabledFormatters(array $enabledFormatters): void
         {
             $this->enabledFormatters = $enabledFormatters;
         }
@@ -65,7 +65,7 @@ in the application::
     {
         // ...
 
-        public function getEnabledFormatters()
+        public function getEnabledFormatters(): array
         {
             // code to configure which formatters to use
             $enabledFormatters = [...];
@@ -92,7 +92,7 @@ to create a configurator class to configure these instances::
             $this->formatterManager = $formatterManager;
         }
 
-        public function configure(EmailFormatterAwareInterface $emailManager)
+        public function configure(EmailFormatterAwareInterface $emailManager): void
         {
             $emailManager->setEnabledFormatters(
                 $this->formatterManager->getEnabledFormatters()
diff --git a/service_container/factories.rst b/service_container/factories.rst
index f6ccd5a1198..9f01e7dc7a6 100644
--- a/service_container/factories.rst
+++ b/service_container/factories.rst
@@ -26,7 +26,7 @@ object by calling the static ``createNewsletterManager()`` method::
 
     class NewsletterManagerStaticFactory
     {
-        public static function createNewsletterManager()
+        public static function createNewsletterManager(): NewsletterManager
         {
             $newsletterManager = new NewsletterManager();
 
@@ -180,7 +180,7 @@ factory service can be used as a callback::
     // ...
     class InvokableNewsletterManagerFactory
     {
-        public function __invoke()
+        public function __invoke(): NewsletterManager
         {
             $newsletterManager = new NewsletterManager();
 
diff --git a/service_container/injection_types.rst b/service_container/injection_types.rst
index 097540bd8f6..6b7b74d1d24 100644
--- a/service_container/injection_types.rst
+++ b/service_container/injection_types.rst
@@ -130,7 +130,7 @@ by cloning the original service, this approach allows you to make a service immu
          * @required
          * @return static
          */
-        public function withMailer(MailerInterface $mailer)
+        public function withMailer(MailerInterface $mailer): self
         {
             $new = clone $this;
             $new->mailer = $mailer;
@@ -224,7 +224,7 @@ that accepts the dependency::
 
     // src/Mail/NewsletterManager.php
     namespace App\Mail;
-    
+
     // ...
     class NewsletterManager
     {
@@ -233,7 +233,7 @@ that accepts the dependency::
         /**
          * @required
          */
-        public function setMailer(MailerInterface $mailer)
+        public function setMailer(MailerInterface $mailer): void
         {
             $this->mailer = $mailer;
         }
diff --git a/service_container/optional_dependencies.rst b/service_container/optional_dependencies.rst
index ca702176341..b981877a942 100644
--- a/service_container/optional_dependencies.rst
+++ b/service_container/optional_dependencies.rst
@@ -113,7 +113,7 @@ In YAML, the special ``@?`` syntax tells the service container that the
 dependency is optional. The ``NewsletterManager`` must also be rewritten by
 adding a ``setLogger()`` method::
 
-        public function setLogger(LoggerInterface $logger)
+        public function setLogger(LoggerInterface $logger): void
         {
             // ...
         }
diff --git a/service_container/parent_services.rst b/service_container/parent_services.rst
index 561721a2a8a..de0d5658b15 100644
--- a/service_container/parent_services.rst
+++ b/service_container/parent_services.rst
@@ -26,7 +26,7 @@ you may have multiple repository classes which need the
             $this->objectManager = $objectManager;
         }
 
-        public function setLogger(LoggerInterface $logger)
+        public function setLogger(LoggerInterface $logger): void
         {
             $this->logger = $logger;
         }
diff --git a/service_container/service_subscribers_locators.rst b/service_container/service_subscribers_locators.rst
index a9579bcfcc3..2fc0ec54fb1 100644
--- a/service_container/service_subscribers_locators.rst
+++ b/service_container/service_subscribers_locators.rst
@@ -87,7 +87,7 @@ a PSR-11 ``ContainerInterface``::
             $this->locator = $locator;
         }
 
-        public static function getSubscribedServices()
+        public static function getSubscribedServices(): array
         {
             return [
                 'App\FooCommand' => FooHandler::class,
@@ -130,7 +130,7 @@ service locator::
 
     use Psr\Log\LoggerInterface;
 
-    public static function getSubscribedServices()
+    public static function getSubscribedServices(): array
     {
         return [
             // ...
@@ -142,7 +142,7 @@ Service types can also be keyed by a service name for internal use::
 
     use Psr\Log\LoggerInterface;
 
-    public static function getSubscribedServices()
+    public static function getSubscribedServices(): array
     {
         return [
             // ...
@@ -159,7 +159,7 @@ typically happens when extending ``AbstractController``::
 
     class MyController extends AbstractController
     {
-        public static function getSubscribedServices()
+        public static function getSubscribedServices(): array
         {
             return array_merge(parent::getSubscribedServices(), [
                 // ...
@@ -176,7 +176,7 @@ errors if there's no matching service found in the service container::
 
     use Psr\Log\LoggerInterface;
 
-    public static function getSubscribedServices()
+    public static function getSubscribedServices(): array
     {
         return [
             // ...
@@ -395,7 +395,7 @@ will share identical locators among all the services referencing them::
     use Symfony\Component\DependencyInjection\ContainerBuilder;
     use Symfony\Component\DependencyInjection\Reference;
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         // ...
 
diff --git a/service_container/synthetic_services.rst b/service_container/synthetic_services.rst
index 5a3ea59d276..59869d5d7f3 100644
--- a/service_container/synthetic_services.rst
+++ b/service_container/synthetic_services.rst
@@ -18,7 +18,7 @@ from within the ``Kernel`` class::
     {
         // ...
 
-        protected function initializeContainer()
+        protected function initializeContainer(): void
         {
             // ...
             $this->container->set('kernel', $this);
diff --git a/service_container/tags.rst b/service_container/tags.rst
index bbe7df1af6b..8bddd65c795 100644
--- a/service_container/tags.rst
+++ b/service_container/tags.rst
@@ -126,7 +126,7 @@ In a Symfony application, call this method in your kernel class::
     {
         // ...
 
-        protected function build(ContainerBuilder $container)
+        protected function build(ContainerBuilder $container): void
         {
             $container->registerForAutoconfiguration(CustomInterface::class)
                 ->addTag('app.custom_tag')
@@ -142,7 +142,7 @@ In a Symfony bundle, call this method in the ``load()`` method of the
     {
         // ...
 
-        public function load(array $configs, ContainerBuilder $container)
+        public function load(array $configs, ContainerBuilder $container): void
         {
             $container->registerForAutoconfiguration(CustomInterface::class)
                 ->addTag('app.custom_tag')
@@ -178,7 +178,7 @@ To begin with, define the ``TransportChain`` class::
             $this->transports = [];
         }
 
-        public function addTransport(\Swift_Transport $transport)
+        public function addTransport(\Swift_Transport $transport): void
         {
             $this->transports[] = $transport;
         }
@@ -304,7 +304,7 @@ container for any services with the ``app.mail_transport`` tag::
 
     class MailTransportPass implements CompilerPassInterface
     {
-        public function process(ContainerBuilder $container)
+        public function process(ContainerBuilder $container): void
         {
             // always first check if the primary service is defined
             if (!$container->has(TransportChain::class)) {
@@ -341,7 +341,7 @@ or from your kernel::
     {
         // ...
 
-        protected function build(ContainerBuilder $container)
+        protected function build(ContainerBuilder $container): void
         {
             $container->addCompilerPass(new MailTransportPass());
         }
@@ -372,16 +372,18 @@ To begin with, change the ``TransportChain`` class::
             $this->transports = [];
         }
 
-        public function addTransport(\Swift_Transport $transport, $alias)
+        public function addTransport(\Swift_Transport $transport, $alias): void
         {
             $this->transports[$alias] = $transport;
         }
 
-        public function getTransport($alias)
+        public function getTransport($alias): ?\Swift_Transport
         {
             if (array_key_exists($alias, $this->transports)) {
                 return $this->transports[$alias];
             }
+
+            return null;
         }
     }
 
@@ -476,7 +478,7 @@ use this, update the compiler::
 
     class TransportCompilerPass implements CompilerPassInterface
     {
-        public function process(ContainerBuilder $container)
+        public function process(ContainerBuilder $container): void
         {
             // ...