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'

---
labels:
summary: 'Component round-robin load balancing module'
...

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

This module enables multiple instances of external components to connect
at the same time, and does round-robin load-balancing of incoming
stanzas.

Example
=======

        Component "test.example.com"
            modules_enabled = { "component_roundrobin" }
            -- Other component options such as secrets here