Error: Unsupported operation: dart:isolate is not supported on dart4web #3

Error: Unsupported operation: dart:isolate is not supported on dart4web
    at Object.throw_ [as throw] (http://localhost:50470/dart_sdk.js:4339:11)
    at Object._unsupported (http://localhost:50470/dart_sdk.js:59179:15)
    at isolate$._ReceivePort.new.get sendPort [as sendPort] (http://localhost:50470/dart_sdk.js:58861:23)
    at iso.Iso.new.run (http://localhost:50470/packages/iso/src/iso.dart.lib.js:74:88)
    at run.next (<anonymous>)
    at runBody (http://localhost:50470/dart_sdk.js:37699:34)
    at Object._async [as async] (http://localhost:50470/dart_sdk.js:37730:7)
    at iso.Iso.new.run (http://localhost:50470/packages/iso/src/iso.dart.lib.js:72:20)
    at geojson.GeoJson.new._parse (http://localhost:50470/packages/geojson/src/geojson.dart.lib.js:390:32)
    at _parse.next (<anonymous>)
    at runBody (http://localhost:50470/dart_sdk.js:37699:34)
    at Object._async [as async] (http://localhost:50470/dart_sdk.js:37730:7)
    at geojson.GeoJson.new.[_parse] (http://localhost:50470/packages/geojson/src/geojson.dart.lib.js:375:20)
    at geojson.GeoJson.new.parse (http://localhost:50470/packages/geojson/src/geojson.dart.lib.js:285:26)
    at nearby_airports._NearbyAirportsPageState.new.loadAirports (http://localhost:50470/packages/flutter_map_demo/airports/nearby_airports.dart.lib.js:359:24)
    at loadAirports.next (<anonymous>)
    at http://localhost:50470/dart_sdk.js:37679:33
    at _RootZone.runUnary (http://localhost:50470/dart_sdk.js:37533:58)
    at _FutureListener.thenAwait.handleValue (http://localhost:50470/dart_sdk.js:32507:29)
    at handleValueCallback (http://localhost:50470/dart_sdk.js:33054:49)
    at Function._propagateToListeners (http://localhost:50470/dart_sdk.js:33092:17)
    at async._AsyncCallbackEntry.new.callback (http://localhost:50470/dart_sdk.js:32818:27)
    at Object._microtaskLoop (http://localhost:50470/dart_sdk.js:37794:13)
    at _startMicrotaskLoop (http://localhost:50470/dart_sdk.js:37800:13)
    at http://localhost:50470/dart_sdk.js:33309:9

Flutter 1.23.0-18.1.pre • channel beta • https://github.com/flutter/flutter.git
Framework • revision 198df796aa (4 weeks ago) • 2020-10-15 12:04:33 -0700
Engine • revision 1d12d82d9c
Tools • Dart 2.11.0 (build 2.11.0-213.1.beta)