Forge version: 14.23.5.2838
Twilight Forest version: 1.12.2-3.8.689-universal
Link to crash log:
https://pastebin.com/5ihxEb2s
https://pastebin.com/xXzJEPpG (with mob grinding utils)

Steps to reproduce:

1. Have any Enderman from Enderman Evolution get damaged.

What I expected to happen:
For the enderman to be killed like normal.

What happened instead:
Crash

Crash is fixed by 3ab2ef5, although it is worth noting that support for the capability in question is built-in by Forge which makes its absence here a little questionable, as the entity involved doesn't have any custom capability handling code.