Undeclared global variable ... 3x

[ghost]

[Mod] travelnet (9f2bbc6/16.03.2019)

2019-04-02 13:23:53: WARNING[Server]: Undeclared global variable "station_network" accessed at /home/thomas/.minetest/mods/travelnet/init.lua:222
2019-04-02 13:23:53: WARNING[Server]: Assignment to undeclared global "station_network" inside a function at /home/thomas/.minetest/mods/travelnet/init.lua:223.
2019-04-02 13:23:53: WARNING[Server]: Undeclared global variable "station_name" accessed at /home/thomas/.minetest/mods/travelnet/init.lua:231

[ghost]

and I see here local formspec =

local formspec = "size[12,"..trheight.."]".. "label[3.3,0.0;"..S("Travelnet-Box")..":]".."label[6.3,0.0;"..S("Punch box to update target list.").."]".. "label[0.3,0.4;"..S("Name of this station:").."]".."label[6.3,0.4;"..minetest.formspec_escape(station_name or "?").."]".. "label[0.3,0.8;"..S("Assigned to Network:").."]" .."label[6.3,0.8;"..minetest.formspec_escape(station_network or "?").."]".. "label[0.3,1.2;"..S("Owned by:").."]" .."label[6.3,1.2;"..minetest.formspec_escape(owner_name or "?").."]".. "label[3.3,1.6;"..S("Click on target to travel there:").."]".. zusatzstr;