The below steps worked for me.
Flutter installation corrupted
The Flutter install directory is in an inconsistent state and that causes all kinds of troubles.
Causes
Unclear
Ways to fix
Run the following commands in the Flutter install directory:
git clean -xfd
git stash save --keep-index
git stash drop
git pull
flutter doctor
Corrupted cache
Especially with plugin packages, it was seen several times that the package in the pub cache was corrupted.
Symptoms
Usually syntax errors at build time about code in dependencies.
Causes
Unknown.
IDEs or editors used by developers might not prevent editing plugin files and when they navigate into plugin code they might accidentally modify the code.
Ways to fix
Run flutter pub cache repair
This might take quite some time and re-downloads every package in the cache, even outdated versions that might not be used anymore by any project on disk.
Delete ~/.pub-cache/hosted
and/or ~/.pub-cache/git
(for Git dependencies). This requires running flutter packages to get in all active projects on your machine afterward.
Delete a specific package or package version. Look up the exact path in the cache for a specific package in the .packages file of your project. For example for firebase_auth
Reference: https://github.com/flutter/flutter/wiki/Workarounds-for-common-issues#flutter-installation-corrupted