Crash when copying a supertank with a yet undetermined locked fluid

Repro steps:

1. Place any super tank
2. Press the "Lock Fluid" button in the GUI. Since there's currently no fluid in the tank, it will only get locked to a concrete fluid when it enters the tank
3. Try copying the super tank somewhere
4. Get a crash

Crash report: https://mclo.gs/1mo99M4

I am on GTNH daily 584