Check for presence of 'avatar_url' key

synapse/push/mailer.py

@@ -259,6 +259,8 @@ class Mailer(object):
 
         sender_state_event = room_state[("m.room.member", event.sender)]
         sender_name = name_from_member_event(sender_state_event)
+        sender_avatar_url = None
+        if "avatar_url" in sender_state_event.content:
             sender_avatar_url = sender_state_event.content["avatar_url"]
 
         # 'hash' for deterministically picking default images: use