How do I fix Attempt to index nil with 'GetChildren'?

Ive tried to put the Mobs folder inside of workspace, it will work but it totally ruins the game. I even set the Primary parts to what it is supposed to be set to but it doesn't work. The Mobs folder is inside ServerStorage.

OUTPUT: Workspace.Tower.Towertesting:7: attempt to index nil with 'GetChildren' - Server - Towertesting:7 16:14:50.033 Stack Begin - Studio 16:14:50.033 Script 'Workspace.Tower.Towertesting', Line 7 - function FindNearestTarget - Studio - Towertesting:7 16:14:50.033 Script 'Workspace.Tower.Towertesting', Line 22 - Studio - Towertesting:22 16:14:50.033 Stack End - Studio

local Tower = script.Parent
local Mobs = workspace.PrimaryPart
local function FindNearestTarget()
	local maxDistance = 15
	local nearestTarget = nil

	for i, target in ipairs(Mobs:GetChildren())do
		local distance = (target.PrimaryPart.Position - Tower.PrimaryPart.Position).Magnitude

		print (target.Name, distance)
		if distance < maxDistance then
			print(target.Name, "Nearest target found")
			nearestTarget = target
			maxDistance = distance
		end
	end

	return nearestTarget
end

while true do
	local target = FindNearestTarget()
	if target then
		target.Humanoid:TakeDamage(3)
	end
	
	task.wait(0.5)
end

I suggest you to change the mobs' humanoids names by another thing like "HumanoidMonster" then in the loop, instead of doing GetChilder(), do workspace:GetDescendants() and the ask if the target have a humanoidmonster then your line of code

It shoould sounds like this

	local Tower = script.Parent
	local Mobs = workspace.PrimaryPart
	local function FindNearestTarget()
        local maxDistance = 15
	    local nearestTarget = nil
	 
	    for i, target in pairs(workspace:GetDescendants()) do
		if target:IsA("Humanoid") and target.Name == "HumanoidMonster" then
	        local distance = (target.Parent.PrimaryPart.Position - Tower.PrimaryPart.Position).Magnitude
	        print (target.Parent.Name, distance)
	        if distance < maxDistance then
	            print(target.Parent.Name, "Nearest target found")
	            nearestTarget = target.Parent
	            maxDistance = distance
	        end
	    end
	 end
	    return nearestTarget
	end
-- some parts of the scripts have been modificated. Copiable

I actually use this strategy for my basic NPCs, so I'm an expert at this.

First of all, the workspace doesn't have a primary part value, if so then probably not intended. I would use workspace.Mobs directly instead of referencing it through that value.

Plus, on top of this, I would recommend directly getting the humanoid and the root part, and returning them, not even the target itself.

Plus, you forgot some checks! I know this is completely unnecessary due to the fact that the folder (or is it a folder??) is meant for the mobs, but it's just in case.

I didn't read through this thoroughly so sorry if I misunderstand some stuff.