lljson.empty_array
decodes to an empty table:
local t = { lljson.null, lljson.empty_array }
print(t[1], t[2])
-- > lljson_constant: 0x0000000000000003 lljson_constant: 0x0000000000000005
local s = lljson.slencode(t)
print(s)
-- > [null,[]]
local ts = lljson.sldecode(s)
print(ts[1], ts[2])
-- > lljson_constant: 0x0000000000000003 table: 0x0000000011ef6718
lljson.slencode()/sldecode()
should be able to recover the exact same table.