object is treated as array after casting a table from object to array

[drinkwithwater]

local rapidjson = require "rapidjson"

local t = rapidjson.object({})
rapidjson.array(t)

local str = rapidjson.encode(rapidjson.object({a=1,b=2}))

print(str) -- expected : {"b":2,"a":1}, but get output : [],