invalid_await_not_required_annotation

The annotation 'awaitNotRequired' can only be applied to a Future-returning function, or a Future-typed field.

The analyzer produces this diagnostic when anything other than a Future-returning function or a Future-typed field or top-level variable is annotated with awaitNotRequired.

The following code produces this diagnostic because the annotation is on a void-returning function:

import 'package:meta/meta.dart';

@awaitNotRequired
void f() {}

Remove the annotation:

void f() {}