mod_roster_command: Fix subscription when the "user JID" is a bare domain. Do not attempt to update the roster when the user is bare domain (e.g. a component), since they don't have rosters and the attempt results in an error: $ prosodyctl mod_roster_command subscribe proxy.example.com contact@example.com xxxxxxxxxxFailed to execute command: Error: /usr/lib/prosody/core/rostermanager.lua:104: attempt to concatenate local 'username' (a nil value) stack traceback: /usr/lib/prosody/core/rostermanager.lua:104: in function 'load_roster' /usr/lib/prosody/core/rostermanager.lua:305: in function 'set_contact_pending_out' mod_roster_command.lua:44: in function 'subscribe'

Introduction
============

This module creates stub configuration files for newly activated hosts.

Configuration
=============

A single option exists, `persisthosts_path`, which is the path where new
stub configuration files are created. It defaults to `"conf.d"`, and is
treated as relative to the configuration directiory [^1] unless set to
an absolute path.

[^1]: usually `/etc/prosody` on \*nix systems