```ruby
class DataForLicenseTypes < ActiveRecord::Migration
  def up
    License.find('by').update_attributes(license_type: 'cc')
    License.find('by-sa').update_attributes(license_type: 'cc')
    License.find('by-nd').update_attributes(license_type: 'cc')
    License.find('by-nc').update_attributes(license_type: 'cc')
    License.find('by-nc-sa').update_attributes(license_type: 'cc')
    License.find('by-nc-nd').update_attributes(license_type: 'cc')
    License.find('cc-sample').update_attributes(license_type: 'cc')

    License.find('public').update_attributes(license_type: 'public')
    License.find('copyright').update_attributes(license_type: 'copyright')

    License.find('gpl').update_attributes(license_type: 'gpl')
    License.find('gpl-v2').update_attributes(license_type: 'gpl')
    License.find('gpl-v3').update_attributes(license_type: 'gpl')
    License.find('copyleft').update_attributes(license_type: 'gpl')
  end

  def down
    # do nothing, when rolling back the next migration erases the column
  end
end
```

Correct migration so it won't fail when db is empty
user
```ruby
class DataForLicenseTypes < ActiveRecord::Migration
  def up
    ['by', 'by-sa', 'by-nd', 'by-nc', 'by-nc-sa', 'by-nc-nd', 'cc-sample'].each do |l|
      License.where(short_name: l).try(:update_attributes, license_type: 'cc')
    end

    License.where(short_name: 'public').try(:update_attributes, license_type: 'public')
    License.where(short_name: 'copyright').try(:update_attributes, license_type: 'copyright')

    ['gpl', 'gpl-v2', 'gpl-v3', 'copyleft'].each do |l|
      License.where(short_name: l).try(:update_attributes, license_type: 'gpl')
    end
  end

  def down
    # do nothing, when rolling back the next migration erases the column
  end
end
```
assistant