migrate to null safty

[kw2019ltd]

Description

All dependencies are migrated to null safety. So we should migrate this package to null safety.
Resources

https://www.youtube.com/watch?v=eBr5tlumwlg&feature=youtu.be
https://medium.com/dartlang/announcing-dart-null-safety-beta-87610fee6730

[pushpendraKh]

This package is discontinued from pub.dev. Do we still expect the migration @AndreHaueisen?

[pushpendraKh]

Someone has pushed https://pub.dev/packages/another_flushbar/ package which is exactly same as this one with null safety support.

[jayeshpansheriya]

you can also use https://pub.dev/packages/awesome_extensions, with some extra feature and with extension, as well as null safety support.