将表单值输入到Rails中的ruby中的控制器中

我有一个带有一些控件的“搜索”页面，下面是搜索页面代码：

<%= form_for :search, :url => { :method => :get, :action => :search } do |f| %>
<table>
      <tr>
         <td align="center" style="vertical-align:top;">
            <h2 style="color:Black; font-size: x-large;">Specs</h2>               
         <table>
            <tr>
               <td align="center">
                  <input type="text" name="tf_Zip" Style="text-align: left;" BackColor="#e5e5e5" Width="180px" ForeColor="Gray" Font-Size="Large">
               </td>
            </tr>             
         </table>
         <table>
            <tr>
               <td>
                  <div class="button">
                    <input type="submit" name="search" value="Search" class="buttonSearch">
                  </div>
               </td>
            </tr>
         </table>
         </td>
         <td align="center" style="vertical-align:top;">
            <h2 style="color:Black; font-size: x-large;">
                    Result
            </h2>
            <% @user_zip.each do |uzr_zip| %>
            <h1><%= uzr_zip.First_Name %></h1>
            <% end %>
            <table id="searchResult" width="100%" runat="server">
                  <tr>
                     <td bgcolor="#CCDBE0">
                        Image:
                     </td>
                     <td bgcolor="#CCDBE0">
                        <%= f.label(:zip, "Mentor") %>
                     </td>
                  </tr>
            </table>
         </td>
      </tr>
</table>
<% end %>

当我尝试将文本框值放入控制器页面时，如下所示

def search
    @students=Students.all
    @blah = params[:search][:tf_Zip]
    end     
    render 'search'
end

然后在下面这行给我一个错误 @blah = params[:search][:tf_Zip]

undefined method `[]' for nil:NilClass

Kindle帮助我。谢谢