diff --git a/src/lib/adapter.ts b/src/lib/adapter.ts
index f1f047f..2199cd2 100644
--- a/src/lib/adapter.ts
+++ b/src/lib/adapter.ts
@@ -170,7 +170,7 @@ export class MongoAdapter implements Adapter {
     fieldIndex: number,
     ...fieldValues: string[]
   ) {
-    const line = new CasbinRule();
+    const line = {};
 
     line.ptype = ptype;