[#7964] don't try to save tag cache if there's no ming session (e.g. test code outsidef of a functional web request)
diff --git a/ForgeGit/forgegit/model/git_repo.py b/ForgeGit/forgegit/model/git_repo.py
index 4c6cfa9..51d300e 100644
--- a/ForgeGit/forgegit/model/git_repo.py
+++ b/ForgeGit/forgegit/model/git_repo.py
@@ -571,7 +571,9 @@
 
         if threshold is not None and time_taken > threshold:
             setattr(self._repo, cache_name, refs)
-            session(self._repo).flush(self._repo)
+            sess = session(self._repo)
+            if sess:
+                sess.flush(self._repo)
 
         return refs