diff --git a/src/Caching/Attribute/Send304IfNotModified.php b/src/Caching/Attribute/Send304IfNotModified.php
index 2d7e960..77a38db 100644
--- a/src/Caching/Attribute/Send304IfNotModified.php
+++ b/src/Caching/Attribute/Send304IfNotModified.php
@@ -30,7 +30,7 @@ public function __construct(...$values)
         );
 
         if (!$values) {
-            throw new InvalidArgumentException(sprintf('The %s attribute needs at least one criterion', __CLASS__));
+            throw new InvalidArgumentException(\sprintf('The %s attribute needs at least one criterion', __CLASS__));
         }
 
         $this->lastmodHelper = new LastmodHelper();
diff --git a/src/Caching/WfdMetaQueries.php b/src/Caching/WfdMetaQueries.php
index 6661681..1e70e4b 100644
--- a/src/Caching/WfdMetaQueries.php
+++ b/src/Caching/WfdMetaQueries.php
@@ -28,6 +28,7 @@
  * )
  *
  * becomes (without the spaces behind the "@"s):
+ *
  * @ ReplaceWithNotModifiedResponse({"@ app_caching_mycontroller_myaction"})
  *
  * with the following service definition:
diff --git a/src/Config/WfdMetaConfigCache.php b/src/Config/WfdMetaConfigCache.php
index b6216e5..9239e97 100644
--- a/src/Config/WfdMetaConfigCache.php
+++ b/src/Config/WfdMetaConfigCache.php
@@ -78,7 +78,7 @@ public function isWfdMetaFresh(): bool
         return $metaQuery->getLastTouched() === $wfdMetaResources['timestamp'];
     }
 
-    public function write($content, array $metadata = null): void
+    public function write($content, ?array $metadata = null): void
     {
         $this->innerCache->write($content, $metadata);
 
diff --git a/src/Config/WfdMetaConfigCacheFactory.php b/src/Config/WfdMetaConfigCacheFactory.php
index 64708cd..be55251 100644
--- a/src/Config/WfdMetaConfigCacheFactory.php
+++ b/src/Config/WfdMetaConfigCacheFactory.php
@@ -47,7 +47,7 @@ public function __construct(ConfigCacheFactoryInterface $configCacheFactory, Met
     public function cache($file, $callback): ConfigCacheInterface
     {
         if (!\is_callable($callback)) {
-            throw new InvalidArgumentException(sprintf('Invalid type for callback argument. Expected callable, but got "%s".', \gettype($callback)));
+            throw new InvalidArgumentException(\sprintf('Invalid type for callback argument. Expected callable, but got "%s".', \gettype($callback)));
         }
 
         $wfdMetaCache = null;
diff --git a/src/DoctrineMetadataHelper.php b/src/DoctrineMetadataHelper.php
index 8019131..c8b707c 100644
--- a/src/DoctrineMetadataHelper.php
+++ b/src/DoctrineMetadataHelper.php
@@ -58,7 +58,7 @@ public function getRootTableName(string $classname): string
     public function getPrimaryKey($entity)
     {
         /** @var $meta ClassMetadata */
-        $meta = $this->metadataFactory->getMetadataFor(\get_class($entity));
+        $meta = $this->metadataFactory->getMetadataFor($entity::class);
 
         return $meta->getFieldValue($entity, $meta->getSingleIdentifierFieldName());
     }
diff --git a/src/MetadataFacade.php b/src/MetadataFacade.php
index a368981..dce4879 100644
--- a/src/MetadataFacade.php
+++ b/src/MetadataFacade.php
@@ -19,7 +19,7 @@ class MetadataFacade
     /**
      * MetadataFacade constructor.
      */
-    public function __construct(Provider $provider, DoctrineMetadataHelper $doctrineMetadataHelper = null)
+    public function __construct(Provider $provider, ?DoctrineMetadataHelper $doctrineMetadataHelper = null)
     {
         $this->provider = $provider;
         $this->doctrineMetadataHelper = $doctrineMetadataHelper;
@@ -37,7 +37,7 @@ public function getLastTouchedForEntity($entity)
         }
 
         return $this->provider->getLastTouchedRow(
-            $this->doctrineMetadataHelper->getRootTableName(\get_class($entity)),
+            $this->doctrineMetadataHelper->getRootTableName($entity::class),
             $this->doctrineMetadataHelper->getPrimaryKey($entity)
         );
     }
diff --git a/src/Util/CriticalSection.php b/src/Util/CriticalSection.php
index 24aac58..7778f61 100644
--- a/src/Util/CriticalSection.php
+++ b/src/Util/CriticalSection.php
@@ -48,7 +48,7 @@ class CriticalSection
      *
      * The lock name is used as key.
      *
-     * @var array<string, integer>
+     * @var array<string, int>
      */
     private static $entranceCount = [];
 
diff --git a/src/Util/ExpirableConfigCache.php b/src/Util/ExpirableConfigCache.php
index 41e1af1..617ed30 100644
--- a/src/Util/ExpirableConfigCache.php
+++ b/src/Util/ExpirableConfigCache.php
@@ -38,7 +38,7 @@ public function __construct($baseFilename, $debug, $timestamp)
         parent::__construct($this->timestampedFile, $debug);
     }
 
-    public function write(string $content, array $metadata = null): void
+    public function write(string $content, ?array $metadata = null): void
     {
         parent::write($content, $metadata);