PatchListLoader: don't swallow exception in automerge

Change-Id: I459e0ae398ebb4890b0d4722572db04d8a379ce3
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java b/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java
index d4131b0..4eede00 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java
@@ -293,6 +293,7 @@
         // an exception most likely means that the merge tree was not created
         // and m.getMergeResults() is empty. This would mean that all paths are
         // unmerged and Gerrit UI would show all paths in the patch list.
+        log.warn("Error attempting automerge " + refName, e);
         return null;
       }