TypeError: this.server.close is not a function when NGINX Unit process itself is terminated

[Thesephi]

Version : 8.2.0-alpha.1

Reproduction steps:

1. start an NGINX Unit app based on somnus
2. monitor the NGINX Unit process log (e.g. tail -F /usr/local/var/log/unit/unit.log)
3. check that the app behaves normally
4. abruptly terminate the NGINX Unit process (e.g. forcefully kill the unitd process)
5. look at unitd log and check that we have the error TypeError: this.server.close is not a function near the end of the log

Expectation: the close method should be exposed & invoked correctly, or if that method is meant to be overwritten by unit-http, then at least it should not throw.