util.multitable: Don't treat false as a missing key 'if not next(some_table)' is a tempting pattern to check whether a table is empty, but we have had multiple bugs in the past where a literal `false` was present as a key, incorrectly matching this test. The correct test is to test for nil, which cannot ever be a key, and means the table is legitimately empty.

-- Prosody IM
-- Copyright (C) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--

module:set_global(); -- we're a global module

-- TODO delete this whole concept