function-always-returns-null

v1.4.0

warning

recommended

configurable

pro+

Warns when a function with nullable return type returns only null.

⚙️ Config

Set ignored-invocations (default is empty) to ignore function expressions within specific function invocations (example).

analysis_options.yaml

dart_code_metrics:
  rules:
    - function-always-returns-null:
        ignored-invocations:
          - useCallback

Example

❌ Bad:

// LINT: This function always returns null. Try checking it for a potential mistake.
String? function() {
  if (value == 2) {
    // ...
  }

  return null;
}

✅ Good:

String? function() {
  if (value == 2) {
    // ...

    return 'some string'; // Correct, returns a non-null value in some cases
  }

  return null;
}

Example with "ignored-invocations"

Config

analysis_options.yaml

dart_code_metrics:
  rules:
    - function-always-returns-null:
        ignored-invocations:
          - useCallback

✅ Good:

void function() {
  useCallback(() { // Correct, ignored
    ...

    return null;
  });
}

Additional Resources

• CWE-670: Always-Incorrect Control Flow Implementation

Related Rules

• avoid-unnecessary-nullable-return-type