Fix default abilities list initialization

Previously, the default value for the abilities list was null, leading to potential NullPointerExceptions. This change initializes the default list as an empty list to prevent such errors.

src/main/java/com/alttd/custommobs/config/MobTypes.java

@@ -53,7 +53,7 @@ public class MobTypes extends AbstractConfig {
             }
             Set<String> keys = configurationSection.getKeys(false);
             keys.forEach(key -> {
-                List<Ability> abilities = config.getStringList(prefix + key, ".abilities", null).stream()
+                List<Ability> abilities = config.getStringList(prefix + key, ".abilities", List.of()).stream()
                         .map(MobTypes.MOB_TYPES::getAbility)
                         .filter(Optional::isPresent)
                         .map(Optional::get)