bug_filer: Add summary for no-op runs

Bug: b/377570481
Change-Id: Ifd4f67bfd99f15c8812d9abe48b88b1b27163cf2
Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/253696
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Reviewed-by: Erik Gilling <konkers@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
diff --git a/recipes/bug_filer.py b/recipes/bug_filer.py
index d0c6761..2347d8f 100644
--- a/recipes/bug_filer.py
+++ b/recipes/bug_filer.py
@@ -276,6 +276,9 @@
         for item in value:
             summary_markdown.append(f'  * {item}')
 
+    if not summary_markdown:
+        summary_markdown.append('Nothing to do')
+
     return result.RawResult(
         summary_markdown='\n'.join(summary_markdown),
         status=common_pb.SUCCESS,