Check for attr rather than classname

atst/filters.py

@@ -1,8 +1,6 @@
 import re
 import datetime
 from flask import current_app as app
-from werkzeug.datastructures import FileStorage
-from atst.models.attachment import Attachment
 
 
 def iconSvg(name):
@@ -48,10 +46,7 @@ def mixedContentToJson(value):
     if (
         isinstance(value, dict)
         and "task_order" in value
-        and (
-            isinstance(value["task_order"]["pdf"], FileStorage)
-            or isinstance(value["task_order"]["pdf"], Attachment)
-        )
+        and hasattr(value["task_order"]["pdf"], "filename")
     ):
         value["task_order"]["pdf"] = value["task_order"]["pdf"].filename
     return app.jinja_env.filters["tojson"](value)