minetest.register_abm({ 
    nodenames = {"default:dirt_with_grass"},
    interval = 2, 
    chance = 1, 
    action = function(pos, node) 
        
        if not minetest.find_node_near(pos, math.random(2, 5), "default:desert_sand") then
        	 return
        end    

 	minetest.add_node(pos,{name="default:drygrass"}) 
end, 
}) 

line 1: attempt to index global 'minetest' (a nil value)
stack traceback:
	t.lua:1: in main chunk
	[C]: ?