It seems that when ensure_nodetree_previews calls duplicate_material,
ntreeLocalize removes the muted node from the copy of the nodetree,
so later in ensure_nodetree_previews nodeFindNodebyName can't find it
and therefore parent is NULL.
With this change, the muted node just doesn't get its preview updated.
Pull Request: https://projects.blender.org/blender/blender/pulls/122776
56ff0d414a