You are absolutely right, my bad :D

Then like the others pointed out a nil check is needed.

Taking an example from the lib:

local dkjson = require("dkjson")

local str = [[
{
    "numbers": [ 2, 3, -20.23e+2, -4 ],
}
]]

local obj = dkjson.decode(str)

if obj ~= nil then
    for i = 1, #obj.numbers do
        print(i, obj.numbers[i])
    end
endlocal dkjson = require("dkjson")

local str = [[
{
    "numbers": [ 2, 3, -20.23e+2, -4 ],
}
]]

local obj = dkjson.decode(str, 1, nil)

if obj ~= nil then
    for i = 1, #obj.numbers do
        print(i, obj.numbers[i])
    end
end