From 5bee0f84d2b6a83e2d64f59a29963e72ad77a81a Mon Sep 17 00:00:00 2001
From: TiynGER <kantemarten@googlemail.com>
Date: Sat, 1 May 2021 01:54:16 +0200
Subject: [PATCH] bugfix: threefold repitition throws nullpointer

If the threefold repitition check is called before enough moves
are saved in the previous board state it throws a nullpointer.
A simple null check solves the problem
---
 src/chess.nim | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/chess.nim b/src/chess.nim
index d7482f6..3ec4543 100644
--- a/src/chess.nim
+++ b/src/chess.nim
@@ -810,6 +810,8 @@ proc isCheckmate*(game: Game, color: Color): bool =
 proc threeMoveRep(game: Game): bool =
   ## Returns true if a 3-fold repitition happened on the last move of the
   ## `game`.
+  if game.previousBoard == []:
+    return false
   var lastState = game.previousBoard[game.previousBoard.high]
   var lastCastleRights = game.previousCastleRights[game.previousBoard.high]
   var reps = 0