From 68682d75b5323ebf45d662dd0d1de563442d147f Mon Sep 17 00:00:00 2001
From: Kim Kulling <kimkulling@users.noreply.github.com>
Date: Fri, 10 Dec 2021 08:39:21 +0100
Subject: [PATCH] Fix nullptr dereferencing from std::shared_ptr

- Finding from fuzzer
- closes https://github.com/assimp/assimp/issues/4237
---
 code/AssetLib/DXF/DXFLoader.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/code/AssetLib/DXF/DXFLoader.cpp b/code/AssetLib/DXF/DXFLoader.cpp
index 3b20678ad..2f1aa6961 100644
--- a/code/AssetLib/DXF/DXFLoader.cpp
+++ b/code/AssetLib/DXF/DXFLoader.cpp
@@ -378,6 +378,11 @@ void DXFImporter::ExpandBlockReferences(DXF::Block& bl,const DXF::BlockMap& bloc
         const DXF::Block& bl_src = *(*it).second;
 
         for (std::shared_ptr<const DXF::PolyLine> pl_in : bl_src.lines) {
+            if (!pl_in) {
+                ASSIMP_LOG_ERROR("DXF: PolyLine instance is nullptr, skipping.");
+                continue;
+            }
+            
             std::shared_ptr<DXF::PolyLine> pl_out = std::shared_ptr<DXF::PolyLine>(new DXF::PolyLine(*pl_in));
 
             if (bl_src.base.Length() || insert.scale.x!=1.f || insert.scale.y!=1.f || insert.scale.z!=1.f || insert.angle || insert.pos.Length()) {