diff --git a/Command/FeedDumpCommand.php b/Command/FeedDumpCommand.php
index 4f25d61..2244325 100644
--- a/Command/FeedDumpCommand.php
+++ b/Command/FeedDumpCommand.php
@@ -39,7 +39,7 @@ class FeedDumpCommand extends Command
      */
     private $feedDumpService;
 
-    public function __construct(RouterInterface $router, FeedDumpService $feedDumpService = null)
+    public function __construct(RouterInterface $router, ?FeedDumpService $feedDumpService = null)
     {
         $this->router = $router;
         $this->feedDumpService = $feedDumpService;
@@ -50,7 +50,7 @@ public function __construct(RouterInterface $router, FeedDumpService $feedDumpSe
     /**
      * {@inheritdoc}
      */
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setDescription('Generate (dump) a feed in an XML file')
diff --git a/DependencyInjection/Compiler/FeedDumpServicePass.php b/DependencyInjection/Compiler/FeedDumpServicePass.php
index fa2bba8..4fc10b9 100644
--- a/DependencyInjection/Compiler/FeedDumpServicePass.php
+++ b/DependencyInjection/Compiler/FeedDumpServicePass.php
@@ -25,7 +25,7 @@ class FeedDumpServicePass implements CompilerPassInterface
     /**
      * {@inheritdoc}
      */
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (!$container->hasAlias('doctrine.orm.entity_manager')) {
             $container->removeDefinition(FeedDumpService::class);
diff --git a/DependencyInjection/Compiler/FeedFormatterPass.php b/DependencyInjection/Compiler/FeedFormatterPass.php
index d59d46d..43b1866 100644
--- a/DependencyInjection/Compiler/FeedFormatterPass.php
+++ b/DependencyInjection/Compiler/FeedFormatterPass.php
@@ -25,7 +25,7 @@ class FeedFormatterPass implements CompilerPassInterface
     /**
      * {@inheritdoc}
      */
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         $formatters = [];
 
diff --git a/DependencyInjection/EkoFeedExtension.php b/DependencyInjection/EkoFeedExtension.php
index 97b2e33..0bd2a20 100644
--- a/DependencyInjection/EkoFeedExtension.php
+++ b/DependencyInjection/EkoFeedExtension.php
@@ -31,7 +31,7 @@ class EkoFeedExtension extends Extension
      * @param array            $configs   An array of configuration settings
      * @param ContainerBuilder $container A container builder instance
      */
-    public function load(array $configs, ContainerBuilder $container)
+    public function load(array $configs, ContainerBuilder $container): void
     {
         $config = $this->processConfiguration(new Configuration(), $configs);
 
@@ -55,7 +55,7 @@ public function load(array $configs, ContainerBuilder $container)
      *
      * @throws \RuntimeException
      */
-    protected function configureHydrator(array $config, ContainerBuilder $container)
+    protected function configureHydrator(array $config, ContainerBuilder $container): void
     {
         if (!$container->hasDefinition($config['hydrator'])) {
             throw new \RuntimeException(sprintf('Unable to load hydrator service "%s"', $config['hydrator']));
diff --git a/Formatter/Formatter.php b/Formatter/Formatter.php
index 2d5a5d6..2415131 100644
--- a/Formatter/Formatter.php
+++ b/Formatter/Formatter.php
@@ -326,7 +326,7 @@ protected function formatWithOptions(ItemFieldInterface $field, ItemInterface $i
      * @param ItemFieldInterface $field   A feed field instance
      * @param ItemInterface|null $item    A feed item instance
      */
-    protected function addAttributes(\DOMElement $element, ItemFieldInterface $field, ItemInterface $item = null)
+    protected function addAttributes(\DOMElement $element, ItemFieldInterface $field, ?ItemInterface $item = null)
     {
         foreach ($field->getAttributes() as $key => $value) {
             if ($item) {