If any of the selected collection entries in the outliner is a linked collection, `outliner_collection_from_tree_element` can return null and it will crash in `BKE_collection_child_find`. This patch handles this case by skipping those entries and modified the warning message to show how many selected entries have failed. ---- This is how the message looks like now: <img width="746" alt="image.png" src="attachments/b91f2a64-7f2d-42d4-8657-7deaf00e90b6"> Pull Request: https://projects.blender.org/blender/blender/pulls/140847