cat

app/models/communication/website/category.rb

@@ -69,7 +69,8 @@ class Communication::Website::Category < ApplicationRecord
   before_create :set_position
 
   def list_of_other_categories
-    website.list_of_categories.reject! { |p| p[:id] == id }
+    new_record? ? website.list_of_categories
+                : website.list_of_categories.reject! { |p| p[:id] == id }
   end
 
   def to_s

app/views/admin/communication/website/categories/_form.html.erb

@@ -23,9 +23,8 @@
                         class: 'js-slug-input',
                         data: { source: '#communication_website_category_name' }
                       } %>
-          <% categories = category.new_record? ? @website.categories : category.list_of_other_categories %>
           <%= f.association :parent,
-                            collection: categories,
+                            collection: category.list_of_other_categories,
                             label_method: ->(p) { sanitize p[:label] },
                             value_method: ->(p) { p[:id] } %>
           <ul>