Needed to type nullability for List parameters correctly.
Change-Id: I55732a34f9e221324a15312985cb83b49a6811a6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/142211
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Srujan Gaddam <srujzs@google.com>