The focus event stream is typed to be non-nullable. Updated the
return of the function passed to reduce in the "_2" version as
well to keep them consistent.
Change-Id: Ic1ae2e027c184d751549c989d60924360139fd5c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/154140
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>