Merge branch 'stable-2.13'

* stable-2.13:
  Support for at-sign (@) in usernames
  VersionedMetaData: Fix deletion of last file in branch
  WatchConfig.Accessor: Add method to delete all watches of an account

Change-Id: I2630ebc2d6bc7c5b68d40f8da2361ae08570790b

gerrit-server/src/main/java/com/google/gerrit/server/git/VersionedMetaData.java

@@ -281,12 +281,7 @@ public abstract class VersionedMetaData {
           return;
         }
 
-        // Reuse tree from parent commit unless there are contents in newTree or
-        // there is no tree for a parent commit.
-        ObjectId res =
-            newTree.getEntryCount() != 0 || srcTree == null
-                ? newTree.writeTree(inserter)
-                : srcTree.copy();
+        ObjectId res = newTree.writeTree(inserter);
         if (res.equals(srcTree) && !update.allowEmpty() && (commit.getTreeId() == null)) {
           // If there are no changes to the content, don't create the commit.
           return;