```ruby
module Spree
  class UserClassHandle
    # Super hack to get around load order.
    def to_s
      Spree.user_class.to_s
    end
  end
end
```

Add some better documentation to the hack.
user
```ruby
module Spree
  # Placeholder for name of Spree.user_class to ensure later evaluation at
  # runtime.
  #
  # Unfortunately, it is possible for classes to get loaded before
  # Spree.user_class has been set in the initializer. As a result, they end up
  # with class_name: "" in their association definitions. For obvious reasons,
  # that doesn't work.
  #
  # For now, Rails does not call to_s on the instance passed in until runtime.
  # So this little hack provides a wrapper around Spree.user_class so that we
  # can basically lazy-evaluate it. Yay! Problem solved forever.
  class UserClassHandle
    # @return [String] the name of the user class as a string.
    # @raise [RuntimeError] if Spree.user_class is nil
    def to_s
      fail "'Spree.user_class' has not been set yet." unless Spree.user_class
      Spree.user_class.to_s
    end
  end
end
```
assistant