fix possible access to empty valie

src/backend/InvenTree/common/forms.py

@@ -51,6 +51,9 @@ class MatchFieldForm(forms.Form):
 
         super().__init__(*args, **kwargs)
 
+        if not file_manager:  # pragma: no cover
+            return
+
         # Setup FileManager
         file_manager.setup()
         # Get columns