Convert Fixnum into String the port number in MySQL
[ci skip] avoid deprecation warning in sample code

Account.find(1, lock: true)
-> DEPRECATION WARNING: Passing options to #find is deprecated. Please build a scope and then call #find on it.
Merge pull request #11839 from chocoby/fix/convert_port_number

Convert Fixnum into String the port number like `db:structure:dump` task in MySQL.
Merge pull request #12560 from sue445/modify_find_lock_sample_code

avoid deprecation warning in sample code [ci skip]
In Relation#empty? use #exists? instead of #count.
Merge pull request #12533 from szimek/use_exists_in_relation_empty

In Relation#empty? use #exists? instead of #count.