Error in Flutter myapp

TypeError: Instance of '_JsonMap': type '_JsonMap' is not a subtype of type 'List'

at Rti._generalAsCheckImplementation [as _as] (http://localhost:55963/dwds/src/injected/client.js:2729:79)
at Rti._installSpecializedAsCheck (http://localhost:55963/dwds/src/injected/client.js:2664:22)
at BuiltJsonSerializers._deserialize$3 (http://localhost:55963/dwds/src/injected/client.js:20953:36)
at BuiltJsonSerializers.deserialize$2$specifiedType (http://localhost:55963/dwds/src/injected/client.js:20938:21)
at BuiltJsonSerializers.deserialize$1 (http://localhost:55963/dwds/src/injected/client.js:20946:19)
at Object._deserializeEvent (http://localhost:55963/dwds/src/injected/client.js:9920:35)
at http://localhost:55963/dwds/src/injected/client.js:26905:26
at _wrapJsFunctionForAsync_closure.$protected (http://localhost:55963/dwds/src/injected/client.js:3893:15)
at _wrapJsFunctionForAsync_closure.call$2 (http://localhost:55963/dwds/src/injected/client.js:13631:12)
at Object._asyncStartSync (http://localhost:55963/dwds/src/injected/client.js:3857:20)
at main__closure8.$call$body$main__closure (http://localhost:55963/dwds/src/injected/client.js:27054:16)
at main__closure8.call$1 (http://localhost:55963/dwds/src/injected/client.js:26892:19)
at StaticClosure._rootRunUnary (http://localhost:55963/dwds/src/injected/client.js:4391:18)
at _CustomZone.runUnary$2$2 (http://localhost:55963/dwds/src/injected/client.js:15254:39)
at _CustomZone.runUnaryGuarded$1$2 (http://localhost:55963/dwds/src/injected/client.js:15201:14)
at _ForwardingStreamSubscription._sendData$1 (http://localhost:55963/dwds/src/injected/client.js:14739:19)
at _ForwardingStreamSubscription._add$1 (http://localhost:55963/dwds/src/injected/client.js:14684:15)
at _ForwardingStreamSubscription._add$1 (http://localhost:55963/dwds/src/injected/client.js:15080:12)
at _MapStream._handleData$2 (http://localhost:55963/dwds/src/injected/client.js:15140:12)
at _ForwardingStreamSubscription._handleData$1 (http://localhost:55963/dwds/src/injected/client.js:15106:20)
at tear_off. (http://localhost:55963/dwds/src/injected/client.js:1637:45)
at StaticClosure._rootRunUnary (http://localhost:55963/dwds/src/injected/client.js:4391:18)
at _CustomZone.runUnary$2$2 (http://localhost:55963/dwds/src/injected/client.js:15254:39)
at _CustomZone.runUnaryGuarded$1$2 (http://localhost:55963/dwds/src/injected/client.js:15201:14)
at CastStreamSubscription.__internal$_onData$1 (http://localhost:55963/dwds/src/injected/client.js:11639:30)
at tear_off. (http://localhost:55963/dwds/src/injected/client.js:1637:45)
at StaticClosure._rootRunUnary (http://localhost:55963/dwds/src/injected/client.js:4391:18)
at _CustomZone.runUnary$2$2 (http://localhost:55963/dwds/src/injected/client.js:15254:39)
at _CustomZone.runUnaryGuarded$1$2 (http://localhost:55963/dwds/src/injected/client.js:15201:14)
at _ControllerSubscription._sendData$1 (http://localhost:55963/dwds/src/injected/client.js:14739:19)
at _DelayedData.perform$1 (http://localhost:55963/dwds/src/injected/client.js:14914:59)
at _PendingEvents_schedule_closure.call$0 (http://localhost:55963/dwds/src/injected/client.js:14973:14)
at StaticClosure._rootRun (http://localhost:55963/dwds/src/injected/client.js:4372:18)
at _CustomZone.run$1$1 (http://localhost:55963/dwds/src/injected/client.js:15246:39)
at _CustomZone.runGuarded$1 (http://localhost:55963/dwds/src/injected/client.js:15189:14)
at _CustomZone_bindCallbackGuarded_closure.call$0 (http://localhost:55963/dwds/src/injected/client.js:15378:25)
at StaticClosure._rootRun (http://localhost:55963/dwds/src/injected/client.js:4376:16)
at _CustomZone.run$1$1 (http://localhost:55963/dwds/src/injected/client.js:15246:39)
at _CustomZone.runGuarded$1 (http://localhost:55963/dwds/src/injected/client.js:15189:14)
at _CustomZone_bindCallbackGuarded_closure.call$0 (http://localhost:55963/dwds/src/injected/client.js:15378:25)
at Object._microtaskLoop (http://localhost:55963/dwds/src/injected/client.js:4220:24)
at StaticClosure._startMicrotaskLoop (http://localhost:55963/dwds/src/injected/client.js:4226:11)
at _AsyncRun__initializeScheduleImmediate_internalCallback.call$1 (http://localhost:55963/dwds/src/injected/client.js:13509:9)

Start by reproducing the error in the Flutter myapp scenario and follow the stack trace to _deserializeEvent in the injected client. Inspect how BuiltJsonSerializers.deserialize handles the event payload and determine why an _JsonMap is treated as a List. Done means the reported TypeError no longer occurs during event deserialization.

Written by the indexing model from the issue text.