Remove unused block arguments

Remove unused variables

Add `assert_nothing_raised` to make clear test case perpose

Use the PORT environment variable for rails server

Only nullify persisted has_one target associations

add Active Job section to instrumentation guide [ci skip]

Get rid of mocha tests in actionpack - part 1

Small fixes [ci skip]

[ci skip]

This example is dependent on the `:end_at` option and has been removed
from `4-2-stable` (d167b811)

Since after 87d1aba3 `dependent: :destroy` callbacks on has_one
assocations run *after* destroy, it is possible that a nullification is
attempted on an already destroyed target:

    class Car < ActiveRecord::Base
      has_one :engine, dependent: :nullify
    end

    class Engine < ActiveRecord::Base
      belongs_to :car, dependent: :destroy
    end

    > car = Car.create!
    > engine = Engine.create!(car: car)
    > engine.destroy! # => ActiveRecord::ActiveRecordError: cannot update a
    >   destroyed record

In the above case, `engine.destroy!` deletes `engine` and *then* triggers the
deletion of `car`, which in turn triggers a nullification of `engine.car_id`.
However, `engine` is already destroyed at that point.

Fixes #21223.

Removed Mocha from ActionView part 1

Conflicts:
	guides/source/security.md

This reverts commit 9876a169.

Reason: Oxford commas are preferred. This is now documented in
the documentation guidelines.

[ci skip] Fix the grammar

This is discussed on https://github.com/rails/rails/pull/21334

* fix command list for thread
* add omitted end of code
* fix description for `continue` and `finish` command

we already have a request, so we should use the methods on the request
to access the path info information

Creates fewer request objects and helps to abstract away from internals

try to remove dependencies on `@env` so we can have more flexible
internals

Remove test helper method to inside test method

Another place to use a request object in NullSessionHash

Remove a link to the site that seems to be gone. [ci skip]

Added docs for CollectionProxy#take 

Followup to #20637.

Remove `MigrationTest#connection` and write `ActiveRecord::Base.connection`
directly to test, because `MigrationTest#connection` is only used in
`test_migration_instance_has_connection`.

May be missed in 5fe14163 commit
Also fixes the broken build

fix syntax error in strip_links example [ci skip]