diff --git a/core/lib/Drupal/Core/Field/PluginSettingsBase.php b/core/lib/Drupal/Core/Field/PluginSettingsBase.php
index c61d96f..aa66214 100644
--- a/core/lib/Drupal/Core/Field/PluginSettingsBase.php
+++ b/core/lib/Drupal/Core/Field/PluginSettingsBase.php
@@ -99,7 +99,7 @@ public function setSetting($key, $value) {
    */
   public function getThirdPartySettings($module = NULL) {
     if ($module) {
-      return isset($this->thirdPartySettings[$module]) ? $this->thirdPartySettings[$module] : NULL;
+      return isset($this->thirdPartySettings[$module]) ? $this->thirdPartySettings[$module] : [];
     }
     return $this->thirdPartySettings;
   }