Rails5中的gem client_side_validation不起作用

Question

如果用户注册，需要验证，该用户名也是客户端唯一的。

• Rails 5 beta 3
• Devisew
• gem client_side_validations

在gemfile中：

gem 'client_side_validations', github: 'DavyJonesLocker/client_side_validations', :branch => 'rails5'

client_side_validations.rb

ActionView::Base.field_error_proc = Proc.new do |html_tag, instance|
  unless html_tag =~ /^<label/
    %{<div class="field_with_errors">#{html_tag}
    <label for="#{instance.send(:tag_id)}" class="message">#{instance.error_message.first}
    </label></div>}.html_safe
  else
    %{<div class="field_with_errors">#{html_tag}
    </div>}.html_safe
  end
end

模型用户

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  has_one :freelancer, dependent: :destroy
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable, :confirmable, :lockable

  validates :username, uniqueness: true       
end

注册/ new.html.erb

<div class="devise_page">
  <div class="title_line">
    <div class="right">
      <%= link_to "Sign In", new_user_session_path %>
     </div>
    <div class="title">Registration</div>
  </div>
<div class="login_page">
  <%= form_for(resource, as: resource_name, url: registration_path(resource_name), validate: true, html: { class: "new_user"} ) do |f| %>
    <div class="item">
      <label for="user_email">E-mail</label>
      <div class="field">
        <%= f.email_field :email, autofocus: true, placeholder: "E-mail" %>
      </div>
    </div>
    <div class="item">
      <label>Nickname</label>
      <div class="field">
        <%= f.text_field :username, placeholder: "Nickname" %> 
      </div>
    </div>
    <div class="item">
    <label>Password</label>
    <div class="field">
      <% if @minimum_password_length %>
        <em>(<%= @minimum_password_length %> characters minimum)</em>
      <% end %><br />
      <%= f.password_field :password, autocomplete: "off", placeholder: "password" %> 
    </div>
    </div>
    <div class="item">
    <label>Password again</label>
    <div class="field">
      <%= f.password_field :password_confirmation, autocomplete: "off", placeholder: "Password again" %>
    </div>
    </div>


    <div class="buttons">
      <%= f.submit "Sign up", class: "button button_green" %>
      <div class="links">
        <%= link_to "Forgot your password?", new_password_path(resource_name) %>  
        <%= link_to "Didn't receive confirmation instructions?", new_confirmation_path(resource_name) %>
      </div>
    </div>
    <% end %>
  </div>
  </div>

如果我输入的字段用户名不是唯一值，则客户端验证不起作用。