From 189cbcaeee5ceb9794188f01686471e0fa9c4106 Mon Sep 17 00:00:00 2001
From: Anton Gladky <gladk@debian.org>
Date: Mon, 27 Jul 2026 16:37:42 +0200
Subject: [PATCH] Fix segfault writing ascii .vtu files with implicit cell type
 arrays

Forwarded: not-yet

NewIterator() returns nullptr for the implicit cell-type arrays used
since VTK 9.6. WriteAsciiData() dereferenced that nullptr via an
unconditional iter->Delete(). Guard it. Closes yade FTBFS.

Gbp-Pq: Name fix_xmlwriter_ascii_implicit_cellarray_segfault.patch
---
 IO/XML/vtkXMLWriter.cxx | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/IO/XML/vtkXMLWriter.cxx b/IO/XML/vtkXMLWriter.cxx
index 413f0f885..030e96cb7 100644
--- a/IO/XML/vtkXMLWriter.cxx
+++ b/IO/XML/vtkXMLWriter.cxx
@@ -1978,7 +1978,10 @@ int vtkXMLWriter::WriteAsciiData(vtkAbstractArray* a, vtkIndent indent)
       ret = 0;
       break;
   }
-  iter->Delete();
+  if (iter)
+  {
+    iter->Delete();
+  }
   return ret;
 }
 
-- 
2.30.2