It's a zero elo patch, and a reasonable safeguard against uncontrolled extreme reductions.
STC:
ELO: -0.08 +-2.0 (95%) LOS: 46.9%
Total: 40000 W: 6728 L: 6737 D: 26535
LTC:
ELO: -0.14 +-1.8 (95%) LOS: 44.0%
Total: 40000 W: 5557 L: 5573 D: 28870
Bench:
7201830
// Null move dynamic reduction based on depth and value
Depth R = 3 * ONE_PLY
+ depth / 4
- + (abs(beta) < VALUE_KNOWN_WIN ? int(eval - beta) / PawnValueMg * ONE_PLY
- : DEPTH_ZERO);
+ + std::min(int(eval - beta) / PawnValueMg, 3) * ONE_PLY;
pos.do_null_move(st);
(ss+1)->skipNullMove = true;