diff --git a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
index a8b1643..4b1dcd4 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -33,7 +33,7 @@ class AnnotatedClassDiscovery implements DiscoveryInterface {
    */
   public function getDefinition($plugin_id) {
     $plugins = $this->getDefinitions();
-    return isset($plugins[$plugin_id]) ? $plugins[$plugin_id] : array();
+    return isset($plugins[$plugin_id]) ? $plugins[$plugin_id] : NULL;
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php b/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php
index 9df7ef6..7a57395 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php
@@ -65,7 +65,7 @@ class CacheDecorator implements DiscoveryInterface {
    */
   public function getDefinition($plugin_id) {
     $definitions = $this->getDefinitions();
-    return isset($definitions[$plugin_id]) ? $definitions[$plugin_id] : array();
+    return isset($definitions[$plugin_id]) ? $definitions[$plugin_id] : NULL;
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Plugin/Discovery/HookDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/HookDiscovery.php
index 3ff05f9..7f74cdb 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/HookDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/HookDiscovery.php
@@ -37,7 +37,7 @@ class HookDiscovery implements DiscoveryInterface {
    */
   public function getDefinition($plugin_id) {
     $plugins = $this->getDefinitions();
-    return isset($plugins[$plugin_id]) ? $plugins[$plugin_id] : array();
+    return isset($plugins[$plugin_id]) ? $plugins[$plugin_id] : NULL;
   }
 
   /**