NodinChan/MobJockeys — comment on commit b5bc2115301f9667b5edac9e166adb8f75ac1c9e
File:  line 0
By Jackcrawf3:

At line 64 in MobJockeysEntityListener, one of these values are null.

"if (plugin.getConfig().getString("MobJockeys.properties." + name + ".mount").equalsIgnoreCase(event.getCreatureType().toString())) {"

Just do a check on every variable in that line to confirm that it exists.