diff --git a/SAS/TMSS/src/tmss/tmssapp/models/specification.py b/SAS/TMSS/src/tmss/tmssapp/models/specification.py
index 60ae93b3054ff5b45ab7727214b734cc6ae98d03..e2a8150450406cdced91b367647296f53075260a 100644
--- a/SAS/TMSS/src/tmss/tmssapp/models/specification.py
+++ b/SAS/TMSS/src/tmss/tmssapp/models/specification.py
@@ -7,6 +7,7 @@ from django.contrib.postgres.fields import ArrayField, JSONField
 from django.contrib.postgres.indexes import GinIndex
 from enum import Enum
 from django_json_widget.widgets import JSONEditorWidget
+import fastjsonschema
 
 #
 # Common
@@ -17,7 +18,7 @@ from django_json_widget.widgets import JSONEditorWidget
 class BasicCommon(Model):
     # todo: we cannot use foreign keys in the array here, so we have to keep the Tags table up to date by trigger or so.
     # todo: we could switch to a manytomany field instead?
-    tags = ArrayField(CharField(max_length=128), size=8, blank=True, help_text='User-defined search keywords for object.')
+    tags = ArrayField(CharField(max_length=128), size=8, blank=True, help_text='User-defined search keywords for object.', default=list)
     created_at = DateTimeField(auto_now_add=True, help_text='Moment of object creation.')
     updated_at = DateTimeField(auto_now=True, help_text='Moment of last object update.')
 
@@ -153,7 +154,6 @@ class Template(NamedCommon):
     class Meta:
         abstract = True
 
-
 # concrete models
 
 class GeneratorTemplate(Template):