Fix backfill when cannot find an event.

`get_pdu` can succeed but return None.

1 files changed, 1 insertions, 1 deletions

diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py

index 3395c9e41e..fe01281c95 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -481,7 +481,7 @@ class FederationClient(FederationBase):
                 defer.DeferredList(deferreds, consumeErrors=True)
             )
             for success, result in res:
-                if success:
+                if success and result:
                     signed_events.append(result)
                     batch.discard(result.event_id)