```ruby
class SetDefaultQuantityForLineItems < ActiveRecord::Migration
  def up
    LineItem.update_all("quantity = 'x'", "quantity IS NULL")
  end

  def down
  end
end
```

Fix (old) migration to work with current model.
user
```ruby
class SetDefaultQuantityForLineItems < ActiveRecord::Migration
  def up
    LineItem.unscoped do
      LineItem.update_all("quantity = 'x'", "quantity IS NULL")
    end
  end

  def down
  end
end
```
assistant