async_value_nullable_pattern

v0.8.0 Warning Fix Riverpod State

Flags AsyncValue(:final value?) when the value type is nullable. The ? pattern matches only when the value is non-null, which is not the same question as whether a value has loaded.

Why use this rule

For an AsyncValue<int?>, a successfully loaded null is a real result. The ? pattern rejects it, so that case silently falls through to the loading or error branch — the UI shows a spinner forever for data that actually arrived. hasValue: true asks the question you meant: has this loaded?

See also: Riverpod - AsyncValue

Don’t

switch (asyncValue) { // AsyncValue<int?>
  case AsyncValue(:final value?): // LINT — a loaded null never matches
    print(value);
  default:
    return const CircularProgressIndicator();
}

Do

switch (asyncValue) { // AsyncValue<int?>
  case AsyncValue(:final value, hasValue: true):
    print(value);
  default:
    return const CircularProgressIndicator();
}

The rule stays silent where the ? pattern is precise:

// Non-nullable value: null can only mean "not loaded"
void fn(AsyncValue<int> asyncValue) {
  switch (asyncValue) {
    case AsyncValue(:final value?):
      print(value);
    default:
      break;
  }
}

// AsyncData.hasValue is always true, so the null check carries the meaning
void onData(AsyncValue<int?> asyncValue) {
  switch (asyncValue) {
    case AsyncData(:final value?):
      print(value);
    default:
      break;
  }
}

Configuration

This rule is in the core preset, so it is on with preset: core, preset: recommended or preset: opinionated.

To turn it off:

many_lints.yaml

rules:
  async_value_nullable_pattern: false

To keep the rule on but skip certain paths, use per-rule exclude.

Related rules

• avoid_build_context_in_providers — Providers outlive widgets, so they should not receive a BuildContext.
• avoid_ref_inside_state_dispose — Avoid accessing ref inside the dispose method of a ConsumerState.
• avoid_ref_read_inside_build — Subscribe in build; do not read once.
• avoid_ref_watch_outside_build — Subscribe only in build; read once everywhere else.