class ActionView::Helpers::FormBuilder

def fields_for_nested_model(name, object, fields_options, block)
  object = convert_to_model(object)
  emit_hidden_id = object.persisted? && fields_options.fetch(:include_id) {
    options.fetch(:include_id, true)
  }
  @template.fields_for(name, object, fields_options) do |f|
    output = @template.capture(f, &block)
    output.concat f.hidden_field(:id) if output && emit_hidden_id && !f.emitted_hidden_id?
    output
  end
end