put core at the beginning so other classes can modify the behavior
Add failing test for ActiveModel::Errors#has_key? method

From the doc, this method should return false and not nil if there is no errors for this key
Move changed_attributes into dirty.rb
Move serialization dirty into serialization.rb
Fix ActiveModel::Errors#has_key? return value
Update ActiveModel::Errors.has_key? test
Merge pull request #13799 from kbrock/better_dirty

Better ActiveRecord hierarchy for Dirty and others
Merge pull request #13795 from bobbus/errors-has-key

Fix ActiveModel::Errors#has_key? returning nil
test boolean and number json param parsing
Merge pull request #13818 from arthurnn/small_test_case

test boolean and number json param parsing
unify param.require tests
Merge pull request #13819 from arthurnn/one_require_test

unify param.require tests
Remove unused assignment to fix warnings in enum test.
Merge pull request #13821 from vipulnsward/remove-assignment-in-test

Remove unused assignment to fix warnings in enum test.
Fix `rake routes` error when `Rails::Engine` with empty routes is mounted; fixes rails/rails#13810

Squash
Merge pull request #13811 from mdesantis/issue-13810

Fixes #13810 `rake routes` error when mount `Rails::Engine` with empty routes
app_rails_loader.rb should check if bin/rails is a File before calling File.read(exe); closes #13825
Merge pull request #13828 from bronzle/apploader-should-check-for-file

app_rails_loader.rb should check if bin/rails is a File before calling F...
Add a test-case for GH #13825
Reordered classes in AR Validation #validates_with example [ci skip]

Person called GoodnessValidator before it was defined.
This change will compile the example correctly.
Merge pull request #13829 from qsymmachus/improve_validates_with_example

Reordered classes in AR Validation #validates_with example [ci skip]