Implements the Observer interface and extends the Subscription class. While the Observer is the public API for consuming the values of an {@link Observable}, all Observers get converted to a Subscriber, in order to provide Subscription-like capabilities such as unsubscribe. Subscriber is a common type in RxJS, and crucial for implementing operators, but it is rarely used as a public API.

The observer used as a stub for subscriptions where the user did not pass any arguments to subscribe. Comes with the default error handling behavior.