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prefer-null-aware-elements

v1.30.0
style
effort: 2m
dart 3.8+
configurable
teams+

Suggests using null-aware elements (?element) instead of checking for a potential null value.

⚙️ Config​

Set ignore-nullable-chains (default is true) to ignore chained nullable property accesses or method invocations (e.g. instance?.prop?.another) (example). Using null-aware elements in such cases can change the meaning of the code.

analysis_options.yaml
dart_code_metrics:
  rules:
    - prefer-null-aware-elements:
        ignore-nullable-chains: true

Example​

❌ Bad:

void fn(int? x, Some? input) {
  final map = {
    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (x != null) "key1": x,

    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (x != null) x: "",

    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (x != null) x: x,

    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (input != null) "key": input.value,

    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (input != null) input.value: "value",
  };

  final list = [
    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (input != null) input,

    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (input != null) input.value,
  ];
}

✅ Good:

void fn(int? x, Some? input) {
  final map = {
    "key1": ?x,
    ?x: "",
    ?x: x,

    "key": ?input.value,
    ?input.value: "value",
  };

  final list = [
    ?input,
    ?input.value,
  ];
}

Example with "ignore-nullable-chains"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - prefer-null-aware-elements:
        ignore-nullable-chains: false

❌ Bad:

void fn(Some? input) {
  final list = [
    // LINT: Prefer null-aware elements (?element) instead of checking for a potential null value.
    if (input != null) input.another, // both `input` and `another` are nullable
  ];
}

class Some {
  int? another;
}
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