UsersController中的ArgumentError＃嵌套属性表单的新错误参数数量（1表示0）

Question

我收到此错误：

我尝试跟随http://guides.rubyonrails.org/form_helpers.html#nested-forms，因为它与我正在尝试创建的内容非常接近

控制器：

class UsersController < ApplicationController

  def new
    @user = User.new
    @user.contact_requests.build
  end

  def create
    @user = User.new(user_params)
  end

  private

    def user_params
      # strong_parameters, which requires us to tell Rails exactly which parameters
      # we want to accept in our controllers
      params.require(:users).permit(:first_name, :last_name, :email, :phone_number, contact_requests_attributes: [:message])
      # params.require(:users).permit!
    end
end

模型：

class User < ActiveRecord::Base
  # before_save { |user| user.email = user.email.downcase }
  has_many :contact_requests
  # validate the presence of the attributes
  validates(:first_name, presence: true)
  validates(:last_name, presence: true)
  validates(:email, presence: true)
  accepts_nested_attributes_for :contact_requests

end

class ContactRequest < ActiveRecord::Base
  belongs_to :user
  validates :user_id, presence: true
  validates :message, presence: true, length: { maximum: 500 }
end

形式：

<section id="contact">
  <div class="container">
    <div class="title-container">Contact Us</div>
    <div class="title-caption">Reach us at (415)-911-9999</div>
    <%= form_for(@user, remote: true, id: "contact-form", class: "contact-input") do |f| %>
      <div class="col-md-12">
        <div class="col-md-6">
          <div class="contact-input-margin form-group">
            <%= f.text_field(:first_name, class: "form-control", placeholder: "First name")%>
          </div>
          <div class="contact-input-margin form-group">
            <%= f.text_field(:last_name, class: "form-control", placeholder: "Last name") %>
          </div>
          <div class="contact-input-margin form-group">
            <%= f.email_field(:email, class: "form-control", placeholder: "Email") %>
          </div>
          <div class="contact-input-margin form-group">
            <%= f.telephone_field(:phone_number, class: "form-control", placeholder: "Phone number") %>
          </div>
        </div>
        <div class="contact-input-margin col-md-6">
          <div class="form-group">
            <%= f.fields_for :contact_requests do |builder| %>
              <%= builder.text_area(:message, class: "form-control contact-margin", rows: "8", placeholder: "Message...") %>
              <% end %>
          </div>
        </div>
      </div>
      <%= f.submit(class: "btn btn-xl") %>
    <% end %>
  </div>
</section>