addToCollection<T>  method 
Add a value to a collection in NyStorage
You can also set allowDuplicates to false to prevent duplicates
Implementation
Future addToCollection<T>(dynamic value,
    {bool allowDuplicates = true}) async {
  return await NyStorage.addToCollection<T>(this,
      item: value, allowDuplicates: allowDuplicates);
}