fix: handle null query params in API + add testing guide

src/app/api/events/route.ts

@@ -65,12 +65,12 @@ export async function POST(request: NextRequest) {
 }
 
 export async function GET(request: NextRequest) {
-  // 1. 解析查询参数
+  // 1. 解析查询参数（将 null 转换为 undefined）
   const searchParams = request.nextUrl.searchParams;
   const queryParams = {
-    year: searchParams.get('year'),
-    limit: searchParams.get('limit'),
-    offset: searchParams.get('offset'),
+    year: searchParams.get('year') || undefined,
+    limit: searchParams.get('limit') || undefined,
+    offset: searchParams.get('offset') || undefined,
   };
 
   // 2. 验证查询参数