To add the Null safety
badge to your README file, simply copy this image tag below
<img src="https://gist.githubusercontent.com/wescosta/26884502a355b6546177db7869b8e19e/raw/037905e760e86d6c7d6150d07edcb15826e3e66b/null-safety-badge.svg" width="80" height="30" alt="This repo supports the null safety language feature.">
Created based on this guide
https://css-tricks.com/custom-styles-in-github-readmes