Empty string is not a valid JSON object, so don't return them in HTTP responses.

synapse/rest/login.py

@@ -70,7 +70,7 @@ class LoginFallbackRestServlet(RestServlet):
     def on_GET(self, request):
         # TODO(kegan): This should be returning some HTML which is capable of
         # hitting LoginRestServlet
-        return (200, "")
+        return (200, {})
 
 
 def _parse_json(request):

synapse/rest/profile.py

@@ -51,7 +51,7 @@ class ProfileDisplaynameRestServlet(RestServlet):
         yield self.handlers.profile_handler.set_displayname(
             user, auth_user, new_name)
 
-        defer.returnValue((200, ""))
+        defer.returnValue((200, {}))
 
     def on_OPTIONS(self, request, user_id):
         return (200, {})
@@ -86,7 +86,7 @@ class ProfileAvatarURLRestServlet(RestServlet):
         yield self.handlers.profile_handler.set_avatar_url(
             user, auth_user, new_name)
 
-        defer.returnValue((200, ""))
+        defer.returnValue((200, {}))
 
     def on_OPTIONS(self, request, user_id):
         return (200, {})

synapse/rest/room.py

@@ -154,14 +154,14 @@ class RoomStateEventRestServlet(RestServlet):
             # membership events are special
             handler = self.handlers.room_member_handler
             yield handler.change_membership(event)
-            defer.returnValue((200, ""))
+            defer.returnValue((200, {}))
         else:
             # store random bits of state
             msg_handler = self.handlers.message_handler
             yield msg_handler.store_room_data(
                 event=event
             )
-            defer.returnValue((200, ""))
+            defer.returnValue((200, {}))
 
 
 # TODO: Needs unit testing for generic events + feedback
@@ -249,7 +249,7 @@ class JoinRoomAliasServlet(RestServlet):
             )
             handler = self.handlers.room_member_handler
             yield handler.change_membership(event)
-            defer.returnValue((200, ""))
+            defer.returnValue((200, {}))
 
     @defer.inlineCallbacks
     def on_PUT(self, request, room_identifier, txn_id):
@@ -416,7 +416,7 @@ class RoomMembershipRestServlet(RestServlet):
         )
         handler = self.handlers.room_member_handler
         yield handler.change_membership(event)
-        defer.returnValue((200, ""))
+        defer.returnValue((200, {}))
 
     @defer.inlineCallbacks
     def on_PUT(self, request, room_id, membership_action, txn_id):