diff --git a/src/stores/compare.ts b/src/stores/compare.ts
index cd8840e..c29a557 100644
--- a/src/stores/compare.ts
+++ b/src/stores/compare.ts
@@ -78,6 +78,7 @@ export const useCompareStore = defineStore("compareStore", {
       } catch (error) {
         apiError(error, "Failed to load the Compare's file name.");
       }
+      return "";
     },
   },
 });
diff --git a/tests/stores/compare.test.js b/tests/stores/compare.test.js
index a99cd87..33cdc86 100644
--- a/tests/stores/compare.test.js
+++ b/tests/stores/compare.test.js
@@ -93,14 +93,14 @@ describe("compareStore", () => {
       expect(result).toBe("file1.csv");
     });
 
-    it("returns undefined for non-existent id", async () => {
+    it("returns empty string for non-existent id", async () => {
       mockGet.mockResolvedValue({
         data: [{ id: 1, name: "file1.csv" }],
       });
 
       const result = await store.getFileName(99);
 
-      expect(result).toBeUndefined();
+      expect(result).toBe("");
     });
   });
 });