Nested_attributes dont appear in my params

I try to include nested_form in one on my model new form.

<%= form_for :master_box, url: master_boxes_path do |f| %>
    <%= f.label :number %><br>
    <%= f.text_field :number %>

    <%= f.fields_for :orders do |o| %>
        <fieldset>
            <%= o.label :number, "Number" %>
            <%= o.text_field :number %>
        </fieldset> 
    <% end %>
    <br>
    <%= f.submit %>
<% end %>

I don't know why when i submit for create my masterbox, my params dont contain orders_attributes.

Here's my models :

class MasterBox < ActiveRecord::Base
  has_many :orders
  accepts_nested_attributes_for :orders
end


class Order < ActiveRecord::Base
  has_many :products
  belongs_to :master_box
end

and my strong paramaters :

def master_box_params
  params.require(:master_box).permit(:number, :number_orders, orders_attributes: [:number])
end

It is pretty simple but i don't understand why i don't have orders_attributes in my params. I have this instead, only "orders" :