await_only_futures  
              
Await only futures.
Details
#AVOID using await on anything which is not a future.
Await is allowed on the types: Future<X>, FutureOr<X>, Future<X>?,
FutureOr<X>? and dynamic.
Further, using await null is specifically allowed as a way to introduce a
microtask delay.
BAD:
dart
main() async {
  print(await 23);
}GOOD:
dart
main() async {
  await null; // If a delay is really intended.
  print(23);
}
Enable
#To enable the await_only_futures rule,
add await_only_futures under linter > rules in your
analysis_options.yaml file:
analysis_options.yaml
yaml
linter:
  rules:
    - await_only_futuresIf you're instead using the YAML map syntax to configure linter rules,
add await_only_futures: true under linter > rules:
analysis_options.yaml
yaml
linter:
  rules:
    await_only_futures: true