Migraiton tool adds casts involving undefined type _

[stereotype441]

Repro steps:

• Check out knaeckeKami/changenotifier_benchmark@4679f8f
• flutter pub get
• Run the migration tool with the --ignore-exceptions flag.

Using the migration tool as of 09481aa, on line 77 of the file lib/print_table.dart, the migration tool suggests adding as _ Function(TestResult). And on line 78, it suggests adding as _ Function(_, dynamic). This doesn't work at all, because there is no type called _.

[stereotype441]

As of 1c7fe71, the null safety migration tool has been removed from active development and retired. No further work on the tool is planned.

If you still need help, or you believe this issue has been closed in error, please feel free to reopen.