Flutter - SQflite '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, dynamic>'

I am trying to save some data with flutter inside the sqflite database, but I am still getting an error that says:

[ERROR:flutter/shell/common/shell.cc(181)] Dart Error: Unhandled
exception:
    type '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, dynamic>'

The error says that the error is inside this function:

Future<RecipesDB> insertRecipe(RecipesDB recipe) async{
    var count = Sqflite.firstIntValue(await _db.rawQuery("SELECT COUNT(*) FROM recipes WHERE name = ?", [recipe.name]));
    if(count == 0){
      recipe.id = await _db.insert("recipes", recipe.toMap()); //"toMap()" function returns the error;
    } else {
      await _db.update("recipes", recipe.toMap(), where: "id = ?", whereArgs: [recipe.id]);
    }
    return recipe;
  }

And this recipe.toMap() points to my class:

import 'dart:convert';

class RecipesDB{
  RecipesDB();

  int id, favorite;
  double workDuration;
  String name, definition, timestamp;

  static final columns = ["id", "name", "definition","duration", "favorite", "timestamp"];

  Map toMap(){
    Map map = {
      "name": name,
      "definition": definition,
      "favorite": favorite,
      "duration": workDuration,
      "timestamp": timestamp
    };

    if(id != null){
      map["id"] = id;
    }

    return map;
  }

  static fromMap(Map map){
    RecipesDB recipes = new RecipesDB();

    recipes.id = map["id"];
    recipes.name = map["name"];
    recipes.definition = map["definition"];
    recipes.workDuration = map["duration"];
    recipes.favorite = map["favorite"];
    recipes.timestamp = map["timestamp"];

    return recipes;
  }

}

I do not know how to solve this error. It would be great, if somebody of you could save me.

Thanks in advance XD!