Cleanup: use plural names for Main lists

Convention was not to but after discussion on 918941483f7e we agree its
best to change the convention.

Names now mostly follow RNA.

Some exceptions:

- Use 'nodetrees' instead of 'nodegroups'
  since the struct is called NodeTree.
- Use 'gpencils' instead of 'grease_pencil'
  since 'gpencil' is a common abbreviation in the C code.

Other exceptions:

- Leave 'wm' as it's a list of one.
- Leave 'ipo' as is for versioning.

1 files changed, 1 insertions, 1 deletions

diff --git a/source/blender/editors/space_outliner/outliner_collections.c b/source/blender/editors/space_outliner/outliner_collections.c
index 7403525c293..7377faa09ac 100644
--- a/source/blender/editors/space_outliner/outliner_collections.c
+++ b/source/blender/editors/space_outliner/outliner_collections.c
@@ -284,7 +284,7 @@ static int collection_delete_exec(bContext *C, wmOperator *op)
 		Collection *collection = BLI_gsetIterator_getKey(&collections_to_edit_iter);
 
 		/* Test in case collection got deleted as part of another one. */
-		if (BLI_findindex(&bmain->collection, collection) != -1) {
+		if (BLI_findindex(&bmain->collections, collection) != -1) {
 			BKE_collection_delete(bmain, collection, hierarchy);
 		}
 	}