CRASH REPORT:

ServerError: AsyncErr: environment_Step: Runtime error from mod 'external_cmd' in callback environment_Step(): ...inetest/worlds/oldserver/worldmods/own_commands/init.lua:672: attempt to index local 'addmute' (a nil value)
2017-12-22 10:51:54: ERROR[Main]: stack traceback:
2017-12-22 10:51:54: ERROR[Main]: 	...inetest/worlds/oldserver/worldmods/own_commands/init.lua:672: in function 'func'
2017-12-22 10:51:54: ERROR[Main]: 	...inetest/worlds/oldserver/worldmods/external_cmd/init.lua:31: in function <...inetest/worlds/oldserver/worldmods/external_cmd/init.lua:8>
2017-12-22 10:51:54: ERROR[Main]: 	/usr/local/share/minetest/builtin/game/register.lua:412: in function </usr/local/share/minetest/builtin/game/register.lua:392>
2017-12-22 10:51:54: ERROR[Main]: stack traceback:


RELEVANT CODE:
func = function(name, param)
                if param == "" then
                minetest.chat_send_player(name, "Usage: /mute <playername>")
                return
                end

local var = param


if minetest.get_player_by_name(var) == nil then
minetest.chat_send_player(name, "This player is not online.")
return
end

if mutedplayers[var] == nil then
local addmute = io.open(minetest.get_worldpath() .. "/permissions/muted/"..var..".txt", "w")
addmute:write("1")
addmute:close()
mutedplayers[var] = 1