#215

backend/app/models/tag.rb

@@ -22,7 +22,7 @@ class Tag < ApplicationRecord
   has_many :parents, through: :reversed_tag_implications, source: :parent_tag
 
   belongs_to :tag_name
-  delegate :name, to: :tag_name
+  delegate :name, to: :tag_name, allow_nil: true
   validates :tag_name, presence: true
 
   enum :category, { deerjikist:  'deerjikist',
@@ -51,6 +51,10 @@ class Tag < ApplicationRecord
     (self.tag_name ||= build_tag_name).name = val
   end
 
+  def has_wiki
+    tag_name&.wiki_page.present?
+  end
+
   def self.tagme
     @tagme ||= find_or_create_by_tag_name!('タグ希望', category: 'meta')
   end
@@ -107,8 +111,9 @@ class Tag < ApplicationRecord
   private
 
   def nico_tag_name_must_start_with_nico
-    if ((category == 'nico' && !(name.start_with?('nico:'))) || 
-        (category != 'nico' && name.start_with?('nico:')))
+    n = name.to_s
+    if ((category == 'nico' && !(n.start_with?('nico:'))) || 
+        (category != 'nico' && n.start_with?('nico:')))
       errors.add :name, 'ニコニコ・タグの命名規則に反してゐます．'
     end
   end