If a map is autostarted, and some supported trigger difficulties are given in the .json file (E.g. jebel_barkal.json), the code attempted to find the default one.
If it isn't given, the code would have accessed an undefined value thus leading to an error.
Now it is looked, whether a default difficulty is given by the map, if yes this one is used, if no, the default difficulty (medium) is used.