Buildcraft version: 7.99.7
Forge version: 13.20.1.2454
Link to crashreport or log (on pastebin or gist, please don't put the entire log here) : https://paste.ee/p/4bvqc
Singleplayer/multiplayer: Singeplayer, Creative (others not tested)

Additional information:
Crash on placing the filler block in the world.

Looks like it was fixed in 96ad84f.

was it? on that line you only removed a null check yet the crash is that something was null so i doubt it's fixed

EDIT: should be fixed after talking about it