Getting nil value in old addon.

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 '•‎​‬‪•'

[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


Should be game.SinglePlayer()

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

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