From 306415391dfe1a304738f307440d7bd79fe93972 Mon Sep 17 00:00:00 2001
From: Mark Haines <mark.haines@matrix.org>
Date: Tue, 1 Dec 2015 11:14:48 +0000
Subject: [PATCH] Only add the user_id if the sender is present

---
 synapse/events/utils.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 666df54114..e634b149ba 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -102,7 +102,9 @@ def format_event_raw(d):
 def format_event_for_client_v1(d):
     d = format_event_for_client_v2(d)
 
-    d["user_id"] = d.get("sender", None)
+    sender = d.get("sender")
+    if sender is not None:
+        d["user_id"] = sender
 
     copy_keys = (
         "age", "redacted_because", "replaces_state", "prev_content",