1 files changed, 46 insertions, 23 deletions
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 042e1788b6..ecbbcf3851 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 import itertools
 import logging
+from collections import defaultdict
 from typing import TYPE_CHECKING, Any, Callable, Dict, List, Tuple
 
 from synapse.api.constants import Membership, PresenceState
@@ -232,29 +233,51 @@ class SyncRestServlet(RestServlet):
         )
 
         logger.debug("building sync response dict")
-        return {
-            "account_data": {"events": sync_result.account_data},
-            "to_device": {"events": sync_result.to_device},
-            "device_lists": {
-                "changed": list(sync_result.device_lists.changed),
-                "left": list(sync_result.device_lists.left),
-            },
-            "presence": SyncRestServlet.encode_presence(sync_result.presence, time_now),
-            "rooms": {
-                Membership.JOIN: joined,
-                Membership.INVITE: invited,
-                Membership.KNOCK: knocked,
-                Membership.LEAVE: archived,
-            },
-            "groups": {
-                Membership.JOIN: sync_result.groups.join,
-                Membership.INVITE: sync_result.groups.invite,
-                Membership.LEAVE: sync_result.groups.leave,
-            },
-            "device_one_time_keys_count": sync_result.device_one_time_keys_count,
-            "org.matrix.msc2732.device_unused_fallback_key_types": sync_result.device_unused_fallback_key_types,
-            "next_batch": await sync_result.next_batch.to_string(self.store),
-        }
+
+        response: dict = defaultdict(dict)
+        response["next_batch"] = await sync_result.next_batch.to_string(self.store)
+
+        if sync_result.account_data:
+            response["account_data"] = {"events": sync_result.account_data}
+        if sync_result.presence:
+            response["presence"] = SyncRestServlet.encode_presence(
+                sync_result.presence, time_now
+            )
+
+        if sync_result.to_device:
+            response["to_device"] = {"events": sync_result.to_device}
+
+        if sync_result.device_lists.changed:
+            response["device_lists"]["changed"] = list(sync_result.device_lists.changed)
+        if sync_result.device_lists.left:
+            response["device_lists"]["left"] = list(sync_result.device_lists.left)
+
+        if sync_result.device_one_time_keys_count:
+            response[
+                "device_one_time_keys_count"
+            ] = sync_result.device_one_time_keys_count
+        if sync_result.device_unused_fallback_key_types:
+            response[
+                "org.matrix.msc2732.device_unused_fallback_key_types"
+            ] = sync_result.device_unused_fallback_key_types
+
+        if joined:
+            response["rooms"][Membership.JOIN] = joined
+        if invited:
+            response["rooms"][Membership.INVITE] = invited
+        if knocked:
+            response["rooms"][Membership.KNOCK] = knocked
+        if archived:
+            response["rooms"][Membership.LEAVE] = archived
+
+        if sync_result.groups.join:
+            response["groups"][Membership.JOIN] = sync_result.groups.join
+        if sync_result.groups.invite:
+            response["groups"][Membership.INVITE] = sync_result.groups.invite
+        if sync_result.groups.leave:
+            response["groups"][Membership.LEAVE] = sync_result.groups.leave
+
+        return response
 
     @staticmethod
     def encode_presence(events, time_now):