Script not deleting models correctly? [ANSWERED]

So I've this tool that is supposed to, on use, delete anything nearby that are inside a certain folder (EventBuildings).

Here's the script (serverscript inside the tool itself)

local eventbuildings = game.Workspace.EventBuildings

local function createselectionbox(adornee)
	--blah blah
end

script.Parent.Activated:Connect(function()
	if script.Parent.InUse.Value == false then
		script.Parent.InUse.Value = true
		wait(0.15)
		script.Parent.Handle.UseNoise:Play()
		local handle = script.Parent.Handle
		local num = 50
		local region = Region3.new(Vector3.new(handle.Position.X - num, handle.Position.Y - num, handle.Position.Z - num), Vector3.new(handle.Position.X + num, handle.Position.Y + num, handle.Position.Z + num))
		local parts = game.Workspace:FindPartsInRegion3(region, nil, math.huge)
		for a, b in pairs(parts) do
			if b:IsA("BasePart") or b:IsA("MeshPart") then
				if b.Parent.ClassName == ("Model") and b.Parent.Parent == eventbuildings then
					createselectionbox(b.Parent)
				elseif b.Parent == eventbuildings then
					createselectionbox(b)
				end
			end
		end
		wait(1)
		for a, b in pairs(parts) do
			if b:IsA("BasePart") or b:IsA("MeshPart") then
				if b.Parent:IsA("Model") and b.Parent.Parent == eventbuildings then
					for c, d in pairs(b.Parent:GetChildren()) do
						table.remove(parts, c)
					end
					b.Parent:Destroy()
				elseif b.Parent == eventbuildings then
					b:Destroy()
				end
			end
		end
		wait(script.Parent.Handle.UseNoise.TimeLength - 0.15)
		script.Parent:Destroy()
	end
end)

Whenever I use the tool I get this error. 16:24:19.949 - Workspace.Old Pocket Watch.Script:28: attempt to index nil with 'IsA'

I tried fixing it by removing those parts from the table which didn't work. I am now completely stumped.