gistfile1.rb

  def update
    milestone = @project.milestones.find(params[:id])
    
    params[:milestone]['invoice_on_completion'] = "0" unless params[:milestone]['invoice_on_completion']
    
    if milestone.update_attributes(params[:milestone])
      respond_to do |format|
        format.js { render :json => milestone }
      end
    else
      respond_to do |format|
        format.js { render :json => milestone.errors.full_messages, :status => :bad_request }
      end
    end
  end

foo ={}
{}
foo['bar'] ||= "0"
"0"
foo
{
"bar" => "0"
}