From 6f9c50df00b6c261d13c10ffad4d9d3af121efda Mon Sep 17 00:00:00 2001
From: Piotr Konopka <piotr.jan.konopka@cern.ch>
Date: Tue, 9 Jul 2024 10:27:18 +0200
Subject: [PATCH] Mergers: avoid a crash if STOP happens without having
 received inputs

---
 Utilities/Mergers/src/FullHistoryMerger.cxx | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Utilities/Mergers/src/FullHistoryMerger.cxx b/Utilities/Mergers/src/FullHistoryMerger.cxx
index 2ed05d46c0e8a..079f557ec83d5 100644
--- a/Utilities/Mergers/src/FullHistoryMerger.cxx
+++ b/Utilities/Mergers/src/FullHistoryMerger.cxx
@@ -145,6 +145,11 @@ void FullHistoryMerger::mergeCache()
 {
   LOG(debug) << "Merging " << mCache.size() + 1 << " objects.";
 
+  if (mFirstObjectSerialized.second.payload == nullptr) {
+    // no objects arrived to the Merger yet, nothing to use.
+    return;
+  }
+
   mMergedObject = object_store_helpers::extractObjectFrom(mFirstObjectSerialized.second);
   assert(!std::holds_alternative<std::monostate>(mMergedObject));
   mObjectsMerged++;