fix: add check for supertypes

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* fix: add check for supertypes for [`avoid-non-null-assertions`](https://dartcodemetrics.dev/docs/rules/common/avoid-non-null-assertion) rule.
 * fix: cover more cases in [`prefer-immediate-return`](https://dartcodemetrics.dev/docs/rules/common/prefer-immediate-return) rule
 * fix: support index expressions for [`no-magic-number`](https://dartcodemetrics.dev/docs/rules/common/no-magic-number) rule.
 * chore: restrict `analyzer` version to `>=2.4.0 <3.5.0`.

lib/src/analyzers/lint_analyzer/rules/rules_list/avoid_non_null_assertion/avoid_non_null_assertion_rule.dart

@@ -3,6 +3,7 @@
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/type.dart';
 
 import '../../../../../utils/node_utils.dart';
 import '../../../lint_utils.dart';

lib/src/analyzers/lint_analyzer/rules/rules_list/avoid_non_null_assertion/visitor.dart

@@ -19,9 +19,14 @@ class _Visitor extends RecursiveAstVisitor<void> {
     if (operand is IndexExpression) {
       final type = operand.target?.staticType;
 
-      return type != null && type.isDartCoreMap;
+      return type is InterfaceType &&
+          (_isMapOrSubclassOfMap(type) ||
+              type.allSupertypes.any(_isMapOrSubclassOfMap));
     }
 
     return false;
   }
+
+  bool _isMapOrSubclassOfMap(DartType? type) =>
+      type != null && type.isDartCoreMap;
 }

test/src/analyzers/lint_analyzer/rules/rules_list/avoid_non_null_assertion/examples/example.dart

@@ -27,5 +27,19 @@ class Test {
     object!.method(); // LINT
 
     object?.method();
+
+    final myMap = MyMap<String, String>();
+    myMap['key']!.contains('other');
+
+    final myOtherMap = MyAnotherMap<String, String>();
+    myOtherMap['key']!.contains('other');
   }
 }
+
+class MyMap<K, V> extends Map<K, V> {
+  void doNothing() {}
+}
+
+class MyAnotherMap<K, V> implements Map<K, V> {
+  void doNothing() {}
+}