made List and Map items non-nullable

[ArpanMondalGITHUB]

made the pigeon/notification.dart file List and Map items non-nullable #942

[chrisbobbe]

Please fix the CI failure and write your commit message according to our style, before we can give this a proper review.

[ArpanMondalGITHUB]

i messed up the branch and the changes that i made for this pr ... i tried to cherry pick but no use ,so i had to delete the branch . can i make a another branch and make a pr for this issue and close this issue .. sorry its my 1st time with all that git command ...from next i will read 1st the git help docs...

[gnprice]

There's nothing to be accomplished by closing this PR and making a new one. Whatever commits you would want to push for the new PR, you can push as an update to this PR instead. See Zulip's Git guide here:
https://zulip.readthedocs.io/en/latest/git/using.html#force-push-changes-to-github-after-you-ve-altered-your-history

If you have questions on how to do that, the #git help channel is the best place to ask.