Allow returning nil from the observable. We know that it will never evaluate to anything interesting, so there's no point creating a brio (which are not free). (Should also probably skip creating a brio if the passed observable is complete and evaluates to nil, i.e. == Rx.EMPTY?).
Propagate state of passed observable. This has just become a slightly more efficient version of a switchMap + toBrio.
nil
from the observable. We know that it will never evaluate to anything interesting, so there's no point creating a brio (which are not free). (Should also probably skip creating a brio if the passed observable is complete and evaluates to nil, i.e. ==Rx.EMPTY
?).