Submitting an extra null element

gistfile1.rb

Couldn't find all Roles with IDs (5, ) (found 1 results, but was looking for 2)

<div id="role-options-<%= user.id %>" class="modal" style="display: none;">
  <%= simple_form_for user, :url => user_path(user), :html => {:method => :put, :class => 'form-horizontal' } do |f| %>
    <div class="modal-header">
      <a class="close" data-dismiss="modal">&#215;</a>
      <h3>Change Role Test</h3>
    </div>
    <div class="modal-body">
      <%= f.input :role_ids, :collection => Role.all, :as => :check_boxes, :label_method => lambda {|t| t.name.titleize}, :label => false, :item_wrapper_class => 'vertical', checked: user.role_ids %>
    </div>
    <div class="modal-footer">
      <%= f.submit "Change Role", :class => "btn" %>
      <a class="btn" data-dismiss="modal" href="#">Close</a>
    </div>
  <% end %>
</div>