Null safety migration

[John-Dormevil]

Hi @letsar Thanks for your work
We actually use your library and we want to contribute by migrating them to null safety what do you think about it ?
#2 😄

[IchordeDionysos]

@letsar you should be unblocked to support null-safety, also the Dart/Flutter team already encourages publishing the migrated packages: See this blog post.

And @John-Dormevil made a great PR to support null safety!
Would be cool if you could take a look at the PR!

[IchordeDionysos]

The new Dart version was just released 😍
https://medium.com/dartlang/announcing-dart-2-12-499a6e689c87

[zs-dima]

any updates are welcome :)

[letsar]

I left a review on the PR ;-)

[Peng-Qian]

@letsar Cool! Please update the awesome package flutter_sticky_header to null-safty~

[letsar]

The v0.3.0 version with null-safety is out! Thanks to @John-Dormevil :-)