Initial commit

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/extension/list_extension.dart

@@ -0,0 +1,11 @@
+/// 可空 List 扩展
+extension ListNullableX on List? {
+  /// 长度，null 视为 0
+  int em() => this?.length ?? 0;
+
+  /// 是否为空（null 也视为空）
+  bool empty() => this == null || this!.isEmpty;
+
+  /// 是否非空
+  bool notEmpty() => this != null && this!.isNotEmpty;
+}