Converting object to an encodable object failed: Instance of 'ScheduleBuildRequest'
#0      _JsonStringifier.writeObject (dart:convert/json.dart:793:7)
#1      _JsonStringStringifier.printOn (dart:convert/json.dart:982:17)
#2      _JsonStringStringifier.stringify (dart:convert/json.dart:967:5)
#3      JsonEncoder.convert (dart:convert/json.dart:345:30)
#4      JsonCodec.encode (dart:convert/json.dart:231:45)
#5      BuildBucketClient._postRequest (package:cocoon_service/src/service/buildbucket.dart:72:63)
<asynchronous suspension>
#6      PresubmitLuciSubscription.post (package:cocoon_service/src/request_handlers/presubmit_luci_subscription.dart:80:11)
<asynchronous suspension>
#7      RequestHandler.service.<anonymous closure> (package:cocoon_service/src/request_handling/request_handler.dart:53:24)
<asynchronous suspension>
#8      SubscriptionHandler.service (package:cocoon_service/src/request_handling/subscription_handler.dart:138:5)
<asynchronous suspension>
#9      main.<anonymous closure>.<anonymous closure> (file:///app/bin/server.dart:304:11)
<asynchronous suspension>