When upgrading a Flutter package for null safety I got this error when running
Error: A library can't opt out of null safety by default, when using sound null safety. // @dart = 2.8 ^^^^^^^^^^^^^^ Failed to load "/Users/xxxxx/test/text_test.dart": Compilation failed
The answer was right there but I was still confused for a while, so I’m adding my answer below.
To solve your problem, remove the following line from text_test.dart:
// @dart = 2.8
Answered By – Suragch
Answer Checked By – David Goodson (FlutterFixes Volunteer)