You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 20200325101528_strip_whitespace_from_user_attributes.rb
    path of file: ./repos/openproject/db/migrate
    
    the code of the file until where you have to start completion: #-- copyright
# OpenProject is an open source project management software.
# Copyright (C) 2012-2024 the OpenProject GmbH
#
    
  def down
    warn <<~WARNING
      We cannot restore leading and trailing white space in user login and mail attributes.
      Please ensure you do not have logins with only leading or trailing white space differences.
    WARNING
  end
end