Why does FormOptionsHelper collection_check_boxes (Rails 4.1.0) create an empty value (value="")?

Question

Ruby on Rails

There are two models Article and Tag associated with HABTM:
article.rb

class Article < ActiveRecord::Base
  has_and_belongs_to_many :tags
end

tag.rb

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :articles
end

I want to display tags as checkboxes in the article editing form:
_form.html.erb

<p>
    <%= f.label "Tags" %><br>
    <%= f.collection_check_boxes :tag_ids, Tag.all, :id, :name%>
  <p>

generated code like this:
html

<p>
    <label for="article_Tags">Tags</label><br>
    <input checked="checked" id="article_tag_ids_1" name="article[tag_ids][]" value="1" type="checkbox"><label for="article_tag_ids_1">Linux</label><input checked="checked" id="article_tag_ids_3" name="article[tag_ids][]" value="3" type="checkbox"><label for="article_tag_ids_3">Ubuntu</label><input checked="checked" id="article_tag_ids_4" name="article[tag_ids][]" value="4" type="checkbox"><label for="article_tag_ids_4">Windows</label><input name="article[tag_ids][]" value="" type="hidden">
  </p>

accordingly, an empty value is passed to params:
Parameters:

"tag_ids"=>["3",
 ""]

UPD:
Thanks for the answer Dimitriy :
An empty value is used to not write processing for deleting related elements if you do not select more than one checkbox.

Answer 1

The problem is in this line

<input name="article[tag_ids][]" value="" type="hidden">

generated by collection_check_boxes
Thanks for answering @Vakiliy : An
empty value is used to avoid writing handling for deleting related items unless more than one checkbox is selected.

Answer 2

I suspect that, in the controller, there is not enough parameter for the white list - tag_ids: []
params.require(:article).permit(...., tag_ids: [])

Answer 3

railscasts.com/episodes/196-nested-model-form-part-1 (outdated screencast, but gives an idea of ​​the problem).
And the solution is here: api.rubyonrails.org/classes/ActiveRecord/NestedAtt...

Answer 4

It is necessary to set include_hidden: falseand then the hidden element will not be added to the form.

<%= f.collection_check_boxes :tag_ids, Tag.all, :id, :name, include_hidden: false %>