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: 20130217072950_add_cgdub_dependencies_updated_at_to_course.rb
    path of file: ./repos/Autolab/db/migrate
    
    the code of the file until where you have to start completion: class AddCgdub
    
  def self.up
    # default to now for easy prepopulation
    add_column :courses, :cgdub_dependencies_updated_at, :datetime, :default => Time.now

    # default really shouldn't be *now*; will be taken care of in before_create going forward
    change_column :courses, :cgdub_dependencies_updated_at, :datetime, :default => nil
  end