Flutter Realtime Database [firebase_database/unknown] Could not convert

Question

I am getting the following error when trying to write data using firebase realtime database:

[firebase_database/unknown] Could not convert

dart-sdk/lib/internal/js_dev_runtime/private/ddc_runtime/errors.dart 294:3 throw packages/firebase_database_web/src/interop/utils/utils.dart 92:5 jsify packages/firebase_database_web/src/interop/utils/utils.dart 80:36 dart-sdk/lib/_internal/js_dev_runtime/private/linked_hash_map.dart 21:7 forEach packages/firebase_database_web/src/interop/utils/utils.dart 79:15 jsify packages/firebase_database_web/src/interop/database.dart 217:56 update packages/firebase_database_web/src/database_reference_web.dart 69:23 update dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 127:5 _async packages/firebase_database_web/src/database_reference_web.dart 67:22 update packages/firebase_database/src/database_reference.dart 120:22 update dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 574:37 _checkAndCall dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 644:10 callMethod dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 648:5 dsend packages/myfinances/controllers/new_expense_controller.dart 42:26 saveExpense dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 127:5 _async packages/myfinances/controllers/new_expense_controller.dart 30:19 saveExpense packages/myfinances/pages/new_expense_page.dart 272:21 packages/flutter/src/gestures/recognizer.dart 275:24 invokeCallback packages/flutter/src/gestures/tap.dart 652:11 handleTapUp packages/flutter/src/gestures/tap.dart 309:5 [_checkUp] packages/flutter/src/gestures/tap.dart 242:7 handlePrimaryPointer packages/flutter/src/gestures/recognizer.dart 630:9 handleEvent packages/flutter/src/gestures/pointer_router.dart 98:7 [_dispatch] packages/flutter/src/gestures/pointer_router.dart 143:9 dart-sdk/lib/_internal/js_dev_runtime/private/linked_hash_map.dart 21:7 forEach packages/flutter/src/gestures/pointer_router.dart 141:17 [_dispatchEventToRoutes] packages/flutter/src/gestures/pointer_router.dart 127:7 route packages/flutter/src/gestures/binding.dart 488:5 handleEvent packages/flutter/src/gestures/binding.dart 468:14 dispatchEvent packages/flutter/src/rendering/binding.dart 439:11 dispatchEvent packages/flutter/src/gestures/binding.dart 413:7 [_handlePointerEventImmediately] packages/flutter/src/gestures/binding.dart 376:5 handlePointerEvent packages/flutter/src/gestures/binding.dart 323:7 [_flushPointerEventQueue] packages/flutter/src/gestures/binding.dart 292:9 [_handlePointerDataPacket] lib/_engine/engine/platform_dispatcher.dart 1289:5 invoke1 lib/_engine/engine/platform_dispatcher.dart 273:5 invokeOnPointerDataPacket lib/_engine/engine/pointer_binding.dart 168:30 [_onPointerData] lib/_engine/engine/pointer_binding.dart 791:20 lib/_engine/engine/pointer_binding.dart 720:7 lib/_engine/engine/pointer_binding.dart 317:9 loggedHandler dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 574:37 _checkAndCall dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 579:39 dcall

code snippet:

class RequestReservationController {
  void addNewReservation(String name, DateTime date, int color) async {
    Reservation reservation = Reservation(name: name, date: DateUtils.dateOnly(date), color: color);
    String nameReservation = '${reservation.name}${reservation.date.day}${reservation.date.month}${reservation.date.year}';
   
    final reservationReference = FirebaseProvider().connection('/Reservations/$nameReservation');
    try{
      await reservationReference.update(reservation.toJson());
    }
    catch(error){
      if (kDebugMode) {
        print(error);
      }
    }
  }
}

class FirebaseProvider{
  connection(String path){
    return FirebaseDatabase.instance.ref().child(path);
  }
}

I have already written data using the realtime database on other occasions and it has always worked. This error only started to appear after updating Flutter to version 78.4.1.