replace regexp global in #url_for
Fix file name in document [ci skip]

This file was renamed in c8a25386d.
Fixing the examples for button_to

The examples do not generate the output they intend to due to not explicitly declaring the hash separations. This causes it to be treated as one parameter instead of the intended two parameters.
Change Class#subclasses doc example
Add ActiveRecord.count documentation when used on group relations
Add documentation for ActiveRecord.select when use strings as arguments
Add example for ActiveRecord::Base.group using a string as argument
Add example for ActiveRecord::Base.joins using a string as argument
Change behaviour with empty array in where clause
Merge pull request #9216 from robertomiranda/where-with-empty-array

Activer Record:  Change behaviour with empty array in where clause
Improve changelog entries in AR

Describe better the changes related to raising errors with empty
array/hash values in where clauses.

[ci skip]
Fix #9168 Initialize NullCookieJar with all options needed for KeyGenerator
Reverting 16f6f25 (Change behaviour with empty array in where clause)
Bump rack dependency to 1.5.2
Merge pull request #9196 from AndreyChernyh/fix-cookies-with-null-session

Fix #9168 Initialize NullCookieJar with all options needed for KeyGenerator
We don't need a CHANGELOG entry for an issue of something that was not released yet
Reverting e170014113 (Change behaviour with empty hash in where clause)
Add missing require to AP
Validations guide: validates_with init clarification.

As discussed with @josevalim on Ruby Rogues Parley.
Clarify ActiveModel::Validator initialization in docs.

As discussed with @josevalim on Ruby Rogues Parley.