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avoid-non-null-assertion

added in: 1.6.0
⚙️

Warns when non null assertion operator (! or “bang” operator) is used for a property access or method invocation. The operator check works at runtime and it may fail and throw a runtime exception.

The rule ignores the index [] operator on the Map class because it's considered the idiomatic way to access a known-present element in a map with []! according to the docs.

note

Use this rule if you want to avoid possible unexpected runtime exceptions.

⚙️ Config​

Set skip-checked-fields (default is false) to allow non-null assertions on fields that are checked to be non-null within an if statement.

dart_code_metrics:
...
rules:
...
- avoid-non-null-assertion:
skip-checked-fields: true

Example​

❌ Bad:

class Test {
String? field;

Test? object;

void method() {
field!.contains('other'); // LINT

object!.field!.contains('other'); // LINT

final map = {'key': 'value'};
map['key']!.contains('other');

object!.method(); // LINT

if (object case int!) { // LINT
// ...
}
}
}

✅ Good:

class Test {
String? field;

Test? object;

void method() {
field?.contains('other');

object?.field?.contains('other');

final map = {'key': 'value'};
map['key']!.contains('other');

object?.method();
}
}