Rubocop

app/models/application_record.rb

@@ -43,11 +43,11 @@ class ApplicationRecord < ActiveRecord::Base
     return unless block_given?
 
     transaction do
-      connection.execute "SET @old_sql_mode = @@sql_mode"
+      connection.execute 'SET @old_sql_mode = @@sql_mode'
       connection.execute "SET SESSION sql_mode = REPLACE(REPLACE(@@sql_mode, 'ONLY_FULL_GROUP_BY,', ''), " \
                          "'ONLY_FULL_GROUP_BY', '')"
       yield
-      connection.execute "SET SESSION sql_mode = @old_sql_mode"
+      connection.execute 'SET SESSION sql_mode = @old_sql_mode'
     end
   end
 end

app/models/tag.rb

@@ -25,7 +25,7 @@ class Tag < ApplicationRecord
   def parent_chain
     Enumerator.new do |enum|
       parent_group = group
-      while parent_group != nil
+      until parent_group.nil?
         enum.yield parent_group
         parent_group = parent_group.group
       end