Proto : all feild optional

gtfs-realtime/proto/gtfs-realtime.proto

@@ -1066,10 +1066,10 @@ message Stop {
 message TripModifications {
 	message Modification {
     // The first stop sequence of the original trip that is to be affected by this modification.
-		required uint32 start_stop_sequence = 1;
+		optional uint32 start_stop_sequence = 1;
 
     // The number of stops which are canceled and replaced by the new_stops. May be zero to indicate no skipped stops.
-		required uint32 num_stops_replaced = 2;
+		optional uint32 num_stops_replaced = 2;
 
     // The number of seconds of delay to add to all departure and arrival times following the end of this modification. If multiple modifications apply to the same trip, the delays accumulate as the trip advances. 
 		optional int32 propagated_modification_delay = 3 [default = 0];
@@ -1116,7 +1116,7 @@ message ReplacementStop {
   optional int32 travel_time_to_stop = 1;
 
   // The replacement stop ID which will now be visited by the trip. May refer to a new stop added using a GTFS-RT Stop message, or to an existing stop defined in the GTFS-Static feed’s stops.txt. The stop MUST have location_type=0 (routable stops).
-  required string stop_id = 2;
+  optional string stop_id = 2;
 
   // The extensions namespace allows 3rd-party developers to extend the
   // GTFS Realtime Specification in order to add and evaluate new features and