Fixing ActiveRecord::Store nil TypeError when using YAML coder

	modified:   activerecord/CHANGELOG.md
	modified:   activerecord/lib/active_record/store.rb
	modified:   activerecord/test/cases/store_test.rb
	modified:   activerecord/test/models/admin/user.rb
	modified:   activerecord/test/schema/schema.rb
Merge branch 'store_yaml_coder' of github.com:oliveiraethales/rails into store_yaml_coder