string value error idk why | Roblox Studio Community | Page 1

i tried fixing it but i dont know the error im lost

type Choice = {item: string, weight: number}

local WeightedSystem = {}
WeightedSystem.__index = WeightedSystem

function WeightedSystem.__call(_: any, list: {Choice})
    return setmetatable({list = list}, WeightedSystem)
end

function WeightedSystem:totalWeight(): number
    local t = 0
    for _, v in ipairs(self.list) do
        t += math.max(0, v.weight)
    end
    return t
end

function WeightedSystem:pick(): string
    local total = self:totalWeight()
    local roll = math.random() * total
    local acc = 0
    for _, v in ipairs(self.list) do
        acc += v.weight
        if roll <= acc then
            return v.item
        end
    end
    return self.list[1].item
end

setmetatable(WeightedSystem, WeightedSystem)

math.randomseed(os.clock() * 1e6)

local selections: {Choice} = {
    {item = "Wood",  weight = 0},
    {item = "Stone", weight = -1},
    {item = "Metal", weight = 0},
}

local picker = WeightedSystem(selections)
local chosen = picker:pick()
chosen():upper()```

#string value error idk why