How to add reaction in Flutter?

I tried several times to use Sandbird’s reaction function.
I tried to update the reaction using ‘applyReactionEvent’ in the message function to add a reaction, but it is not updated on the sendbird server and only applied to the chat room.
And also i tried to use ‘addReaction’ of channel function, but i get error message that is ‘Unhandled Exception: type ‘Null’ is not a subtype of type ‘int’ in type cast’. and check in ‘package:sendbird_sdk/features/reaction/reaction_event.g.dart’, the problem occurs because there is no ‘updated_at’ value.
How can I solve this?