The bug: A package may not list itself as a dependency

If you named your app with the same name as any packages in pubspec.yaml.
When running:
$ flutter packages get
You will have the bug: "A package may not list itself as a dependency"
For example, I created an app named firebase_messaging and in pubspec.yaml I also included the package named firebase_messaging

To fix this, you have to change the name of your app.