diff --git a/src/app/entity.ts b/src/app/entity.ts
index 39797c5..9bf5ed9 100644
--- a/src/app/entity.ts
+++ b/src/app/entity.ts
@@ -48,7 +48,7 @@ export abstract class Entity<T extends Data> {
     }
 
     isPersisted(): boolean {
-        return this.__id !== ''
+        return this.__id !== undefined && this.__id !== ''
     }
 
     toString() {