A simple custom error type for marking the end of a [Promistream](https://promistream.cryto.net/). You'd usually only need this module when you're implementing a custom source stream.
If you just want a stream that produces a value every time one is requested, and that doesn't need to clean up any external resources like file handles or network connections, use the [simple-source](https://www.npmjs.com/package/@promistream/simple-source) module instead.
