fix: throw exception when an item isn't found by searchByUniqueName

lib/src/clients/items_client.dart

@@ -1,4 +1,5 @@
 import 'dart:convert';
+import 'dart:io';
 
 import 'package:warframestat_client/warframestat_client.dart';
 
@@ -122,14 +123,20 @@ class WarframeItemsClient extends WarframestatClient {
   }
 
   /// Pulls an item useing it's uniqueName.
+  ///
+  /// Returns null when an item with the uniqueName doesn't exist.
   Future<Item> searchByUniqueName(String uniqueName) async {
     final encodedUniqueName = Uri.encodeQueryComponent(uniqueName);
-    final item = await _get<Map<String, dynamic>>(
+    final request = await _get<Map<String, dynamic>>(
       '/$encodedUniqueName/',
       query: {'by': 'uniqueName'},
     );
 
-    return toItem(item);
+    if (request['code'] == HttpStatus.notFound) {
+      throw ItemNotFound(uniqueName);
+    }
+
+    return toItem(request);
   }
 
   Future<T> _get<T>(String path, {Map<String, dynamic>? query}) async {

lib/src/utils/exceptions.dart

@@ -0,0 +1,13 @@
+/// {@template item_not_found}
+/// Item exceptions thrown when an item was not found.
+/// {@endtemplate}
+class ItemNotFound implements Exception {
+  /// {@macro item_not_found}
+  const ItemNotFound(this.item);
+
+  /// Item name or uniqueName.
+  final String item;
+
+  @override
+  String toString() => '$item was not found.';
+}

lib/src/utils/utils.dart

@@ -1,2 +1,3 @@
+export 'exceptions.dart';
 export 'item_categories.dart';
 export 'items_utils.dart';