On line 164 in scripts/skills/throw_dirt_skill.nut it says: if (!_user.isHiddenToPlayer() && (_targetTile.IsVisibleForPlayer || this.knockToTile.IsVisibleForPlayer))
This leads to an error in the log because knockToTile does not exist in this.
Solution:
Change that line to: if (!_user.isHiddenToPlayer() && _targetTile.IsVisibleForPlayer)