Ruby: 2.0.0p0 , Rails: 3.2.13, redcarpet: 2.2.2 application_helper.rb

def markdown(text)                                                                                                     
markdown_render = Redcarpet::Render::HTML.new(:hard_wrap => true, :no_styles => true)
markdown = Redcarpet::Markdown.new(markdown_render, :autolink => true, :no_intro_emphasis => true) 
markdown.render(text).to_html.html_safe   
end 

app/views/questions/new.html.erb

<%= simple_form_for @question do |f| %>
<%= f.input :title, :input_html => { :class => "span6" } %> 
<%= markdown(@question.content) %> 
<%= f.button :submit, :class => 'btn-primary' %> 
<%= link_to 'Cancel', @question.id.blank? ? questions_path : question_path(params[:question]), :class => "btn btn-danger" %>
<% end %>

可是这样就会报错：wrong argument type nil (expected String) 将<%= markdown(@question.content) %> 改成<%= markdown(@question.content.to_s) %>后又报错：undefined methodto_html' for "":String，然后又将application_helper中的markdown.render(text).to_html.html_safe改为markdown.render(text).html_safe`后，没有了 content 输入框，只有 title 输入框。 求指导。。