Fix T68135: Do not return NULL/None when converting an object to a mesh.

Does not make sense in the use-cases of that function, especially since
we don't know whether it is actually due to an error, or some glitch
(like an empty curve).

Think we always want to get a mesh when using either operator
conversion, or the `bpy.data.meshes.new_from_object` function.

Note that an assert was also added to ensure we do try to convert from a
valid 'geometry' object type.

1 files changed, 6 insertions, 2 deletions

diff --git a/source/blender/blenkernel/intern/mesh_convert.c b/source/blender/blenkernel/intern/mesh_convert.c
index ae9cf874676..ee060a117dc 100644
--- a/source/blender/blenkernel/intern/mesh_convert.c
+++ b/source/blender/blenkernel/intern/mesh_convert.c
@@ -1216,10 +1216,14 @@ Mesh *BKE_mesh_new_from_object_to_bmain(Main *bmain,
                                         Object *object,
                                         bool preserve_all_data_layers)
 {
+  BLI_assert(ELEM(object->type, OB_FONT, OB_CURVE, OB_SURF, OB_MBALL, OB_MESH));
+
   Mesh *mesh = BKE_mesh_new_from_object(depsgraph, object, preserve_all_data_layers);
   if (mesh == NULL) {
-    /* Unable to convert the object to a mesh. */
-    return NULL;
+    /* Unable to convert the object to a mesh, return an empty one. */
+    Mesh *mesh_in_bmain = BKE_mesh_add(bmain, ((ID *)object->data)->name + 2);
+    id_us_min(&mesh_in_bmain->id);
+    return mesh_in_bmain;
   }
 
   /* Make sure mesh only points original datablocks, also increase users of materials and other