Flutter SQFlite convert Class toJson()

Question

I am building a SQFlite database for my app but I have a problem with the creation of my DB. Converting my class toJson() the code throws me the following errors:

Database file:

  Future<Entries> create(Entries entries) async {
    final db = await instance.database;

    final id = await db.insert(tableFavs, entries.toJson());
  }

Error (at entries.toJson()): A value of type 'Set' can't be returned from the method 'toJson' because it has a return type of 'Map<dynamic, dynamic>'.

Here is my class:

import 'package:flutter/material.dart';

const String tableFavs = 'favorites';

class EntryFields {
  static late String id = '_id';
  static late String name = '_name';
  static late String navigation = '_navigation';
}

class Entries {
  final int id;
  final String name;
  final Widget navigation;

  Entries({
    required this.id,
    required this.name,
    required this.navigation,
  });

  Map<Object> toJson() => {
        EntryFields.id = id,
        EntryFields.name = name,
        EntryFields.navigation = navigation,
      };
  }

Does anyone knows how to fix this?