Ruby on rails RubyonRails-prawn和prawnto错误

在ruby on rails应用程序prawn中，使用prawnto生成pdf会引发一些错误

 def generate_report

    generate_report = params[:report_type]

# puts(generate_report)

if generate_report == "1"
       # get count of all successful downloads
  @total_downloads=StatisticDownload.where("DownloadSuccess=?","1").count
  #puts(@total_downloads)
  # get all downloads grouped by date
  @downloads  = StatisticDownload.select("date(Date) as downloaded_date, count(id) as count").where("DownloadSuccess=?","1").group("date(Date)")
  respond_to do |format|
    format.pdf { render :layout => false }
   end  
         end 

生成报告.pdf.prawn中的代码

        pdf.move_down(30) 
      book =  @downloads.map do |item|
     [
       item.downloaded_date,
         item.count
     ]
      end
         pdf.table book, :border_style => :grid,
        :row_colors => ["FFFFFF", "DDDDDD"],
        :headers => ["downloaded_date", "count"],
        :align => { 0 => :left, 1 => :right, 2 => :right, 3 => :right }

/admin/generate_报告提供一个空白页作为输出

/admin/generate_report.pdf给出了一个错误

  You have a nil object when you didn't expect it!
  You might have expected an instance of Array.
  The error occurred while evaluating nil.map
  Extracted source (around line #2):

     1: pdf.move_down(30) 
      2: book =  @downloads.map do |item|
      3:  [
    4:   item.downloaded_date,
     5:   item.count

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如何纠正此错误

可能值得一看，在本教程之后，如果您没有专业订阅，则必须订阅watch。

更改控制器中的代码，如下所示：respond_to do | format | format.pdf do render:layout=>false end end现在可以正常工作了。现在的问题是在视图上设置文件的样式，它会生成一个错误undefined method headers='for undefined method align=>'。您能告诉我为什么会发生这种情况吗？