anchor.diff:     *
      * [obj] is the object to be inserted.
      */
  -  Future insert(T obj, {WriteConcern writeConcern}) {
  +  Future insert(obj, {WriteConcern writeConcern}) {
       return mongoDb.insert(collection, obj, writeConcern: writeConcern ?? this.writeConcern);
     }
   
  
positive.code:    *
     * [obj] is the object to be saved.
     */
    Future save(T obj, {WriteConcern writeConcern}) {
      return mongoDb.save(collection, obj, writeConcern: writeConcern ?? this.writeConcern);
    }
  
  
negative.code:    *
     * [objs] are the objectes to be inserted.
     */
    Future insertAll(List objs, {WriteConcern writeConcern}) {
      return mongoDb.insertAll(collection, objs, writeConcern: writeConcern ?? this.writeConcern);
    }
  
  