Fixes #11773 when using includes combined with select, the select statement was overwritten.
flatten and flatten! methods for ActiveSupport::Duration
No need to require rbconfig as we are using Gem.ruby
Merge pull request #12503 from arunagw/removed-unused-require

No need to require rbconfig as we are using Gem.ruby
Merge pull request #12480 from iwiznia/master

flatten and flatten! methods for ActiveSupport::Duration
no reason to do this column addition and subtraction business
Revert "Merge pull request #12480 from iwiznia/master"

This reverts commit e5f5a838b96a362534d9bb60d02334439ed9784c, reversing
changes made to d7567f3290a50952494e9213556a1f283a6cf3a0.
Some fixes in docs [ci skip]

Update a link to point to right section in api docs

Fix a typo
Fix a writing mistake

A small mistake found in the line of ```The default error is "can't be empty"``` for ```:presence``` helper. ```empty``` word changed to ```blank```.
Merge pull request #12512 from sbagdat/patch-1

Fix a writing mistake
Merge pull request #12507 from malavbhavsar/doc_patch

Some fixes in docs [ci skip]
Merge pull request #11791 from versioncontrol/includes_with_persistent_select

Includes with persistent select, fixes #11773
Add arel to Gemfile
Address ORA-00972: identifier is too long
Oracle database does not support release savepoint
Oracle currently handles empty string as null