From ef634b7eea60334e4ade70ba74e0ee1af3be6e35 Mon Sep 17 00:00:00 2001
From: Alex Dutka <97711898+dutkalex@users.noreply.github.com>
Date: Fri, 6 Mar 2026 13:49:49 +0100
Subject: [PATCH 1/3] Add null pointer case

---
 src/t8_forest/t8_forest.cxx | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/t8_forest/t8_forest.cxx b/src/t8_forest/t8_forest.cxx
index f66522f471..24d5e43e39 100644
--- a/src/t8_forest/t8_forest.cxx
+++ b/src/t8_forest/t8_forest.cxx
@@ -1466,6 +1466,11 @@ t8_gloidx_t
 t8_forest_element_face_neighbor (t8_forest_t forest, t8_locidx_t ltreeid, const t8_element_t *elem, t8_element_t *neigh,
                                  t8_eclass_t neigh_eclass, int face, int *neigh_face)
 {
+  int dummy = 0;
+  if (neigh_face == nullptr) {
+    neigh_face = &dummy;
+  }
+  
   /* Get a pointer to the tree to read its element class */
   const t8_tree_t tree = t8_forest_get_tree (forest, ltreeid);
   const t8_eclass_t eclass = tree->eclass;

From 0ac3bae33e7e9902ab9846131f1994d04a45b04f Mon Sep 17 00:00:00 2001
From: Alex Dutka <97711898+dutkalex@users.noreply.github.com>
Date: Fri, 6 Mar 2026 13:57:02 +0100
Subject: [PATCH 2/3] Update documentation

---
 src/t8_forest/t8_forest_general.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/t8_forest/t8_forest_general.h b/src/t8_forest/t8_forest_general.h
index b57878b920..9301e3eb98 100644
--- a/src/t8_forest/t8_forest_general.h
+++ b/src/t8_forest/t8_forest_general.h
@@ -861,7 +861,7 @@ t8_forest_element_neighbor_eclass (t8_forest_t forest, t8_locidx_t ltreeid, cons
  *                          the data could be modified arbitrarily.
  * \param [in] neigh_eclass The eclass of \a neigh.
  * \param [in] face         The number of the face along which the neighbor should be constructed.
- * \param [out] neigh_face  The number of the face viewed from perspective of \a neigh.
+ * \param [out] neigh_face  The number of the face viewed from perspective of \a neigh. Can be nullptr.
  * \return The global tree-id of the tree in which \a neigh is in.
  *        -1 if there exists no neighbor across that face.
  */

From e55d09e26f0a997480e040e3aaa3847f23bee450 Mon Sep 17 00:00:00 2001
From: Alex Dutka <97711898+dutkalex@users.noreply.github.com>
Date: Fri, 6 Mar 2026 13:59:12 +0100
Subject: [PATCH 3/3] indent

---
 src/t8_forest/t8_forest.cxx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/t8_forest/t8_forest.cxx b/src/t8_forest/t8_forest.cxx
index 24d5e43e39..51a29d1254 100644
--- a/src/t8_forest/t8_forest.cxx
+++ b/src/t8_forest/t8_forest.cxx
@@ -1470,7 +1470,7 @@ t8_forest_element_face_neighbor (t8_forest_t forest, t8_locidx_t ltreeid, const
   if (neigh_face == nullptr) {
     neigh_face = &dummy;
   }
-  
+
   /* Get a pointer to the tree to read its element class */
   const t8_tree_t tree = t8_forest_get_tree (forest, ltreeid);
   const t8_eclass_t eclass = tree->eclass;