title: Why does the error occur after the Flutter Clean command?
body: <p>After using the Flutter Clean command, packages cannot be found and too many errors appear.</p>
  <p>After running the &quot;flutter pub get&quot; command, the problems are corrected.
  It wasn't like this before, what could be the reason for this?</p>
  <p>Flutter 2.0.2 • channel stable •
  Framework • revision 8962f6dc68 (6 days ago) • 2021-03-11 13:22:20 -0800
  Engine • revision 5d8bf811b3
  Tools • Dart 2.12.1</p>
  <p><a href="https://i.stack.imgur.com/8euXZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8euXZ.png" alt="After flutter clean" /></a></p>