The entity class for this instance of Nymph.
Headers that will be sent with every request.
These are used by Tilmeld for authentication.
And optional PubSub client instance.
Return null or empty array instead of error when entity/ies not found.
Add your class to this instance.
This will create a class that extends your class within this instance of Nymph and return it. You can then use this class's constructor and methods, which will use this instance of Nymph.
Because this creates a subclass, don't use the class returned from
getEntityClass to check with instanceof. Instead, use the base class
that you passed into this method.
The entity cache.