At:
https://docs.oracle.com/javase/9/tools/java.htm#GUID-3B1CE181-CD30-4178-9602-230B800D4FAE__CBBIJCHG
I see:

```
--list-modules [modulename[,modulename...]]
Lists the observable modules and exits.
```

But --list-modules takes no args.

The replacement flag --describe-module is missing.