diff --git a/workflow/engine/classes/class.pmScript.php b/workflow/engine/classes/class.pmScript.php
index df0ab928b..5d40faa7e 100644
--- a/workflow/engine/classes/class.pmScript.php
+++ b/workflow/engine/classes/class.pmScript.php
@@ -123,7 +123,7 @@ class PMScript
     /**
      * Affected fields
      */
-    public $affected_fields;
+    public $affected_fields = [];
 
     public $scriptExecutionTime = 0;