util.datamapper: Don't include empty unwrapped arrays
Since there is no way to distinguish an empty such array from a
zero-length array. Dropping it seems like the least annoying thing to
do.
For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends
If you have luarocks available on your platform, install the following:
- luaexpat
- luasocket
- luafilesystem
- luasec