回形针 - 错误

Question

我正在创建一个允许用户登录后上传文档的应用程序。当我尝试点击视图页面时，我不断获得NoMethodError in Pages#about  First argument in form cannot contain nil or be empty
对于我的观看代码

  <%= form_for @document, html: { multipart: true } do |f| %>
      <%= f.file_field :attachment %>
  <% end %>

这是我的pages_controller.rb

class PagesController < ApplicationController

def new 
    @document = Document.new
end

def create
    @document = Document.new(document_params)
    @document.save
end

private
def document_params
    params.require(:document).permit(:attachment).merge(user_id: current_user.id)
end
end

这是我的user.rb

    class User < ActiveRecord::Base
    has_many :documents

end

这是我的document.rb

Class Document < ActiveRecord::Base
    belongs_to :user # -> allows you to call @user.documents
    has_attached_file :attachment 



@user.documents.each do |document|
    image_tag document.attachment.url #-> outputs the image
end