Can someone help me fix this error: "Attempt to index a nil value"?

I have a 3D Perlin noise generator, and I decided to make a script that will generate 3D perlin noise around the player based of where they walk. But I encountered an error that I can't fix. At line 53 it errors, And tells me "Attempt to index a nil value". Here is the script:

local chunks = {}

local function chunkExists(chunkX, chunkZ, chunkY) -- Check's if a chunk exists
   		spawn(function()
	local isNil = false

  -- if not chunks[chunkX] then
  --    chunks[chunkX] = {}
	  
  -- end
   if not chunks[chunkX] then
       chunks[chunkX] = {}
     --  return false
   end
   if not chunks[chunkX][chunkZ] then
       chunks[chunkX][chunkZ] = {}
     --  return false
   end
   if not chunks[chunkX][chunkZ][chunkY] then
       chunks[chunkX][chunkZ][chunkY] = {}
       --return false
   end

  -- if isNil == false then
       return chunks[chunkX][chunkZ][chunkY]
  -- end
	end)
end

local function roundTo(number, roundToNumber) -- Give it a value and it'll round it to the target's multiple, e.g 12 goes to 8, 17 goes to 16.
	return number - (number % roundToNumber)
end

local function CheckPos(X, Z, Y)
	spawn(function() -- We use spawn function because if we don't then every time this function is called then the (all) the client(s) that are running the game will freeze
		local RoundedX = roundTo(X, 32)
		local RoundedZ = roundTo(Z, 32)
		local RoundedY = roundTo(Y, 32)
		
		--print(" X: "..RoundedX.." Z: "..RoundedZ.." Y: "..RoundedY)
		--print(RoundedZ)
		--print(RoundedY)
		
		for x = -32, 32 do
			for z = -32, 32 do
				for y = -32, 32 do
					local cx = RoundedX + x
					local cz = RoundedZ + z
					local cy = RoundedY + y
					
					if not chunkExists(cx, cz, cy) == true then
						--print("x: "..cx.." z: "..cz.." y: "..cy)
						chunks[cx][cz][cy] = true
						
					end
				end
			end
		end
	end)
end

spawn(function()
	while true do
		wait(1)
		--print("hh")
		for i, v in pairs(game:GetService("Players"):GetChildren()) do
			local C = nil
			local HRP = nil
			
			pcall(function()
				if v.Character then
					C = v.Character
				else
					C = nil
				end
			end)
			
			if C ~= nil then
				pcall(function()
					if C:FindFirstChild("HumanoidRootPart") then
						HRP = C:FindFirstChild("HumanoidRootPart")
						
					else
						HRP = nil
					end
				end)
			end
			
			if HRP ~= nil then
				CheckPos(HRP.Position.X, HRP.Position.Z, HRP.Position.Y)
			end
		end
	end
end)

I am still having this issue can someone PLEASE help me?