`GroupGetResult` has redundant types


Seems like `Option>` is just `Vec` with extra steps. Is there information communicated by `None` that isn't communicated by `[ ]`? If so, we should document that. If not, we should improve the interface so you don't have to check for both `None` and `.len() > 0` when using it.

Start by locating `GroupGetResult` and tracing how callers distinguish `None` from an empty `Vec`. Determine whether the two states communicate different information, then document that behavior or propose a simpler interface and update the affected callers and tests. No file or test paths are named in the issue.

Written by the indexing model from the issue text.