Fix #388. Update signature of getEntityClass().

webprofiler/src/Entity/Decorators/Config/ConfigEntityStorageDecorator.php

@@ -229,7 +229,7 @@ class ConfigEntityStorageDecorator extends EntityDecorator implements ConfigEnti
   /**
    * {@inheritdoc}
    */
-  public function getEntityClass($bundle = NULL) {
+  public function getEntityClass(?string $bundle = NULL) : string {
     return $this->getOriginalObject()->getEntityClass($bundle);
   }