TMSS-163: only set jsoneditorwidget for Subtask instances, not for lists, to prevent exceptions

SAS/TMSS/src/tmss/tmssapp/serializers/scheduling.py

@@ -157,10 +157,11 @@ class SubtaskSerializerJSONeditorOnline(RelationalHyperlinkedModelSerializer):
         import json
 
         try:
-            schema = self.instance.specifications_template.schema
-            self.fields['specifications_doc'] = serializers.JSONField(
-                style={'template': 'josdejong_jsoneditor_widget.html',
-                       'schema': json.dumps(schema)})
+            if isinstance(self.instance, models.Subtask):
+                schema = self.instance.specifications_template.schema
+                self.fields['specifications_doc'] = serializers.JSONField(
+                    style={'template': 'josdejong_jsoneditor_widget.html',
+                           'schema': json.dumps(schema)})
         except Exception as e:
             # todo: Shall we use one of the default templates for the init?
             logger.exception('Could not determine schema, hence no fancy JSON form. Expected for list view.')