Fixed subcategory validation in promotion create

app/controllers/promotions_controller.rb

@@ -28,7 +28,7 @@ class PromotionsController < ApplicationController
   # POST /promotions.json
   def create
     @promotion = Promotion.new(promotion_params)
-    @promotion.subcategory_id = nil if !@promotion.nil? && @promotion.subcategory_id.zero?
+    @promotion.subcategory_id = nil if !@promotion.subcategory_id.nil? && @promotion.subcategory_id.zero?
     source =
       if @promotion.category_id.present? || @promotion.subcategory_id.present?
         "a la #{@promotion.subcategory_id.present? ? 'sublínea' : 'línea'} #{@promotion.subcategory_id.present? ? Category.find(@promotion.subcategory_id).category : @promotion.category.category}"