Ok, said simply, how do I make it so if the player presses down, if there is a dense object there, it returns, but if there ISN'T a dense object there, they simply move south. The main purpose of doing this is to make it so they don't face against a wall. This is what I have tried so far:

client/South()
var/turf/T = get_step(mob,SOUTH)
if(T.density)
return
else ..()

//This really made nothing happen, I fiddled with this for a bit, but to no avail.

I want to make this work so if you move south for an example. Any help would be appreciated.