runtime null

```
runtime error: Cannot read null.volume
proc name: reconcile air (/datum/pipeline/proc/reconcile_air)
source file: datum_pipeline.dm,216
usr: null
src: /datum/pipeline (/datum/pipeline)
call stack:
/datum/pipeline (/datum/pipeline): reconcile air()
/datum/pipeline (/datum/pipeline): process()
Air (/datum/subsystem/air): process pipenets()
Air (/datum/subsystem/air): fire()
```