ActsAsTaggableOn with collection_check_boxes

_form.html.erb

<%= form_for(@sundae) do |f| %>
  <!--
    collection_check_boxes requires 4 parameters, the last two are methods that access
    the value and text from the collection, respectively. Hence the need for
    SundaesHelper.valid_flavors!
  -->
  <%= f.collection_check_boxes(:flavor_list, Sundae::FLAVORS, :itself, :itself) do |b| %>
    <!-- FYI: I use Bootstrap 4, so I customized how the checkboxes would render -->
    <div class="form-check">
      <label class="form-check-label"><%= b.check_box class: 'form-check-input' %> <%= b.value %></label>
    </div>
  <% end %>

  <%= f.submit %>
<% end %>

sundae.rb

class Sundae < ApplicationRecord
  FLAVORS = ['Chocolate', 'Vanilla', 'Strawberry', 'Grapenut']
  
  acts_as_taggable_on :flavors
end

sundaes_controller.rb

class SundaesController < ApplicationController
  # ...
  
  private
  
  def sundae_params
    params.require(:outreach).permit(:flavor_list => [])
  end
end