Getting nil value in old addon.

[WinMillion]

I'm attempting to convert an addon to GMOD 13, but an error shows up;

[ERROR] 
  1. unknown - [C]:-1

Error in hook PlayerFootstep: addons/floras bf3 vault/lua/autorun/client/css_legs.lua:901: attempt to call global 'SinglePlayer' (a nil value)
stack traceback:
	addons/floras bf3 vault/lua/autorun/client/css_legs.lua:901: in function 'v'
	lua/includes/modules/hook.lua:84: in function <lua/includes/modules/hook.lua:67>
	[C]: in function '•&#8298;&#8206;&#8301;&#8203;&#8236;&#8303;&#8234;•'

[ERROR] 
  1. unknown - [C]:-1

on this line of lua:

function SlideFoot( ply, pos, foot, sound, volume, rf )

	if not SinglePlayer() then
	
	if ply.Sliding then
	return true
	end
	
	end
	
end

[c👌de_g🎷]

Should be game.SinglePlayer()

[FireWolf]

Should the SinglePlayer() code not be game.SinglePlayer() ([url]https://wiki.garrysmod.com/page/game/SinglePlayer[/url])?

[Gmod4phun]

This page will help you with most of the problems [url]http://wiki.garrysmod.com/page/Updating_Scripts_From_GMod_12_to_GMod_13[/url]
The addon has been fixed before, but good luck with that