https://github.com/mongodb/mongo/blob/cdeaaed41d92487a9aa2f679e581e2b8b7b5c1dd/src/mongo/db/commands/query_cmd/bulk_write.idl#L78 you call getUpdate() instead of getNsIndex which is confusing cause it looks like its going to return the filter or a updateRef or something. also each op type has a different accessor for the same info