`pry-byebug` is in the gemspec so we expect this file to exist sometimes.

This allows us to indent the text properly without the whitespace making it into the resulting string.

Looking at the sinatra extensions guide[1] it looks like you're meant to use `set` to set this kind of class-level state.

The value has to be initialised to nil otherwise you get `NoMethodError: undefined method `serializer_class'`, I guess because the accessor method is only created when `set` is called.

[1] http://sinatrarb.com/extensions.html#setting-options-and-other-extension-setup

Following the sinatra extensions guide[1] it looks like this is how you're meant to do it.

Unfortunately this results in a breaking change in pliny because pliny apps will have to switch their endpoint classes to use `register` instead of `helper` (see the change in the template in this commit). But it fixes a compatibility issue between pliny and sinatra 2.1 where the latter has switched its internal behaviour, using `prepend` rather than `include` for helpers, meaning the `self.included` hook is no longer being called.

[1] http://sinatrarb.com/extensions.html#extending-the-dsl-class-context-with-sinatraregister