Fix small bugs in tree ops (from !163)
Fix 3 bugs we encountered when calling rng_max_element_by
because of changes from !163 (merged) - I didn't catch them earlier because I tested the PR with only a subset of all my plots, sorry about that!
Two changes are simple typos catched by my linter.
The addition of returnType
to GetDataMember
I'm not 100% sure about - but it seems to work.