Terrain Editing Plugin Issue?

Upon downloading and installing Anaminus's Better Brush, it generates a error, which I cannot seems to fix. The output from Studio is stated below:

18:37:50.394 - C:/Users/Chance/AppData/Local/Roblox/Plugins/BetterBrush/Be:10: attempt to index local 'Terrain' (a nil value)

The plugin icon exists, but is fully visible on the toolbar.

If anyone could tell me why it is throwing that error and a fix, i'd greatly appreciate it

Code snip below. First segment of 400 lines.

local Plugin = PluginManager():CreatePlugin()
local Toolbar = Plugin:CreateToolbar("Terrain")
local ActivateButton = Toolbar:CreateButton("", "Brush", "brush.png")
local Mouse = Plugin:GetMouse()

local plugin_loaded = false
local plugin_active = false

local Terrain = game.Workspace.Terrain
local SetCell = Terrain.SetCell
local SetCells = Terrain.SetCells
local GetCell = Terrain.GetCell
local AutowedgeCells = Terrain.AutowedgeCells
local WorldToCellPreferSolid = Terrain.WorldToCellPreferSolid

local MAX_HEIGHT = Terrain.MaxExtents.Max.Y

local brushRadius = 4
local maxBrushRadius = 16
local minBrushRadius = 1

local heightOffset = 0
local maxHeightOffset = 32
local minHeightOffset = -32

local brushMaterial = 1
local clearAbove = false
local fillBelow = true
local autoSmooth = true

local Region3i = Region3int16.new
local Vector3i = Vector3int16.new
local function R3(a,b,c,x,y,z)
	return Region3i(
		Vector3i(a,b,c),
		Vector3i(x,y,z)
	)
end