From 58480f5b318a6b08ce0b9b0b2c1237f6814f3f0f Mon Sep 17 00:00:00 2001
From: biwa <6475593+biwa@users.noreply.github.com>
Date: Sun, 9 Jul 2023 14:18:24 +0200
Subject: [PATCH] Visual Mode: fixed a crash when toggling visual vertex slope
 picking and the map contains double-sided linedefs without a front sidedef.
 Fixes #928

---
 Source/Plugins/BuilderModes/VisualModes/VisualVertexSlope.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Source/Plugins/BuilderModes/VisualModes/VisualVertexSlope.cs b/Source/Plugins/BuilderModes/VisualModes/VisualVertexSlope.cs
index ae20f593..358eece0 100644
--- a/Source/Plugins/BuilderModes/VisualModes/VisualVertexSlope.cs
+++ b/Source/Plugins/BuilderModes/VisualModes/VisualVertexSlope.cs
@@ -37,7 +37,7 @@ namespace CodeImp.DoomBuilder.VisualModes
 
 			angle = line.GetAngle();
 
-			if (ld.Front.Sector != s)
+			if (ld.Front?.Sector != s)
 				clockwise = !clockwise;
 		}
 	}