如何使用 Lua 处理 JSON 中的 null 值？

我正在 Asterisk PBX 中使用 Lua。在处理 JSON 字符串时，我遇到了以下问题。

为什么将 JSON 中的 "null" 值转换为 Lua 中的函数类型？

如何处理这种情况？ 因为在 JSON 中没有值意味着 null，而在 Lua 中 nil 意味着什么都没有。

local json = require("json")
local inspect = require("inspect")
local myjson_str='{"Sms":{"key":"xxxxxxxxxxxxxxxxxxxxx","to":"{caller}","senderid":null,"type":"Simple","content":"Your request has been accepted in Previous Miss call. We get back to you very soon."}}'

local myjson_table = json.decode(myjson_str)
print(type(myjson_table["Sms"]["senderid"]))
print(myjson_table)
print(inspect(myjson_table))
print(json.encode(myjson_table))

上述代码的输出是

function
table: 0xf5e770
{
  Sms = {
    content = "Your request has been accepted in Previous Miss call. We get back to you very soon.",
    key = "xxxxxxxxxxxxxxxxxxxxx",
    senderid = <function 1>,
    to = "{caller}",
    type = "Simple"
  }
}
{"Sms":{"type":"Simple","key":"xxxxxxxxxxxxxxxxxxxxx","senderid":null,"content":"Your request has been accepted in Previous Miss call. We get back to you very soon.","to":"{caller}"}}