attempt to perform arithmetic (mul) on nil and number. Why is this happening? Can someone fix?

I am making this game where you collect crystals as a intvalue, and you can sell them. I keep getting this error and i don't know why. I have defined prices btw.

local function sellGems(otherPart)
	local player = game.Players:FindFirstChild(otherPart.Parent.Name)
	if player then 
		local amount = 0
		for _, type in pairs(player.Inventory:GetChildren()) do
			amount = amount + (prices[type.Name] * type.Value)
			type.Value = 0
		end
		player.leaderstats.Money.Value = player.leaderstats.Money.Value + amount
	end
end