Some of the the resource metadata properties are collections/maps.

I think currently we are not consistent and in some cases we return null if there is no value (e.g.
BlobInfo and BucketInfo) and in some cases we return an empty collection (e.g. ProjectInfo).

My preference would be to never return null for a collection as I think the value of being able to
distinct the case of "unassigned" and "assigned and empty" is very small and does not justify
the cost for checking for null and empty.

In any case, I think we should be consistent.

/cc @mziccard @ajkannan @mderka