Omit displayname or avatar_url if they aren't set instead of returning null (#7497)

Per https://github.com/matrix-org/matrix-doc/issues/1436#issuecomment-410089470 they should be omitted instead of returning null or "". They aren't marked as required in the spec.

Fixes https://github.com/matrix-org/synapse/issues/7333



Signed-off-by: Aaron Raimist <aaron@raim.ist>

changelog.d/7497.bugfix

+When sending `m.room.member` events, omit `displayname` and `avatar_url` if they aren't set instead of setting them to `null`. Contributed by Aaron Raimist.

synapse/handlers/message.py

@@ -484,9 +484,13 @@ class EventCreationHandler(object):
 
                 try:
                     if "displayname" not in content:
-                        content["displayname"] = yield profile.get_displayname(target)
+                        displayname = yield profile.get_displayname(target)
+                        if displayname is not None:
+                            content["displayname"] = displayname
                     if "avatar_url" not in content:
-                        content["avatar_url"] = yield profile.get_avatar_url(target)
+                        avatar_url = yield profile.get_avatar_url(target)
+                        if avatar_url is not None:
+                            content["avatar_url"] = avatar_url
                 except Exception as e:
                     logger.info(
                         "Failed to get profile information for %r: %s", target, e