Looks like there's a issue with the cooling/heating network from Dubs Central Heating when there are multiple floors.

Reproduction:
1. Go into "Dev quickstart"
2. Place "Small ladder down"
3. Place air-con pipes
4. Place heating pipes
5. NullReferenceException triggers

Repro Screenshot: https://imgur.com/h0j4Bk4
Logs: https://gist.github.com/HugsLibRecordKeeper/8c21c233294651cc8105173492634b40

The errors stop occurring if I remove the ladder and destroy the second map, so it definitely seems like there's an issue with how the heating / cooling network gets handed across multiple floors.