LUA_VERSION=5.3 ./test.sh

./awall/iptables.lua:121: attempt to concatenate a table value (local 'rule')
stack traceback:
    ./awall/uerror.lua:25: in metamethod '__concat'
    ./awall/iptables.lua:121: in method 'dumpfile'
    ./awall/iptables.lua:44: in method 'print'
    ./awall/init.lua:164: in method 'print'
    ./awall-cli:275: in upvalue 'dump'
    ./awall-cli:280: in local 'filedump'
    ./awall-cli:302: in upvalue 'f'
    ./awall/uerror.lua:20: in function <./awall/uerror.lua:20>
    [C]: in function 'xpcall'
    ./awall/uerror.lua:19: in function 'call'
    ./awall-cli:156: in main chunk
    [C]: in ?

It explodes in IPTables:dumpfile:

      for i, chain in sortedkeys(chains) do
         for i, rule in ipairs(chains[chain]) do
            iptfile:write('-A '..chain..' '..rule..'\n')
         end
      end

…because rule is a table.

I used inspect to print the table rule:

{
  <metatable> = {
    __index = <function 1>
  }
}

(from redmine: issue id 8377, created on 2018-01-04)