creator tag value is nil?

I'm trying to make a tool that drops a boulder upon clicking, and I keep getting an error message from my leader board saying "attempt to index local "killer" (a nil value) ".

--function that inserts that boulder/creator tag
local tool = script.Parent
local boulder = script.BScript
local clickEvent = tool.ClickEvent
local clickEventConnection
local bCreator = tool.Parent.Parent.Name

local function createPart(location)
	local part = Instance.new("Part", game.Workspace)
	part.Name = "Boulder"
	part.Shape = "Ball"
	part.Size = Vector3.new(13,13,13)
	local mesh = Instance.new("FileMesh", part)
	mesh.MeshId = "http://www.roblox.com/asset/?id=1290033"
	mesh.TextureId = "http://www.roblox.com/asset/?id=1290030"
	mesh.Scale = Vector3.new(10, 10, 10)
	local bscript = boulder:Clone()
	bscript.Parent = part
	bscript.Disabled = false
	local creatorTag = Instance.new('ObjectValue', part)
	creatorTag.Value = bCreator
	creatorTag.Name = 'creator'
	part.CFrame = location
end

--Script that gets duplicated into the boulder

local boulder = script.Parent
local creatorTag = boulder:WaitForChild("creator")

local DebrisService = Game:GetService('Debris')

local function ApplyTags(target)
	while target:FindFirstChild('creator') do
		target.creator:Destroy()
	end

	local creatorTagClone = creatorTag:Clone()
	DebrisService:AddItem(creatorTagClone, 1.5)
	creatorTagClone.Parent = target
end


function onTouch(hit)
	local humanoid = hit.Parent:findFirstChild("Humanoid")
	if humanoid ~= nil then
		if hit.Parent:findFirstChild("Boulder Shield")== nil then
			humanoid.Health = humanoid.Health - 70
			ApplyTags(humanoid)
		end
	end
end
script.Parent.Touched:connect(onTouch)


wait(5)
script.Parent:Destroy()