Update gomatrixserverlib

vendor/manifest

@@ -98,7 +98,7 @@
 		{
 			"importpath": "github.com/matrix-org/gomatrixserverlib",
 			"repository": "https://github.com/matrix-org/gomatrixserverlib",
-			"revision": "8e7504f3b62366e621525c962314f53c045512e3",
+			"revision": "785a53c41170526aa7a91a1fc534afac6ce01a9b",
 			"branch": "master"
 		},
 		{

vendor/src/github.com/matrix-org/gomatrixserverlib/event.go

@@ -119,6 +119,10 @@ func (eb *EventBuilder) Build(eventID string, now time.Time, origin ServerName,
 		EventID        string     `json:"event_id"`
 		OriginServerTS Timestamp  `json:"origin_server_ts"`
 		Origin         ServerName `json:"origin"`
+		// This key is either absent or an empty list.
+		// If it is absent then the pointer is nil and omitempty removes it.
+		// Otherwise it points to an empty list and omitempty keeps it.
+		PrevState *[]EventReference `json:"prev_state,omitempty"`
 	}
 	event.EventBuilder = *eb
 	if event.PrevEvents == nil {
@@ -131,6 +135,16 @@ func (eb *EventBuilder) Build(eventID string, now time.Time, origin ServerName,
 	event.Origin = origin
 	event.EventID = eventID
 
+	if event.StateKey != nil {
+		// In early versions of the matrix protocol state events
+		// had a "prev_state" key that listed the state events with
+		// the same type and state key that this event replaced.
+		// This was later dropped from the protocol.
+		// Synapse ignores the contents of the key but still expects
+		// the key to be present in state events.
+		event.PrevState = &emptyEventReferenceList
+	}
+
 	// TODO: Check size limits.
 
 	var eventJSON []byte