diff --git a/src/module/timeLabel.js b/src/module/timeLabel.js
index e6f5cba..de11aff 100644
--- a/src/module/timeLabel.js
+++ b/src/module/timeLabel.js
@@ -251,4 +251,5 @@ export const mapTimestampToAxisTicksByFormat = (timeStampArr, timeFormat) => {
   if (timeStampArr) {
     return timeStampArr.map((ts) => moment(ts).format(timeFormat));
   }
+  return [];
 };
diff --git a/tests/unit/module/timeLabel.test.js b/tests/unit/module/timeLabel.test.js
index 6d4ad25..0816df8 100644
--- a/tests/unit/module/timeLabel.test.js
+++ b/tests/unit/module/timeLabel.test.js
@@ -168,7 +168,7 @@ describe("mapTimestampToAxisTicksByFormat", () => {
     expect(result[0]).toBe("2023/01/15");
   });
 
-  it("returns undefined for falsy input", () => {
-    expect(mapTimestampToAxisTicksByFormat(null, "YYYY")).toBeUndefined();
+  it("returns empty array for falsy input", () => {
+    expect(mapTimestampToAxisTicksByFormat(null, "YYYY")).toEqual([]);
   });
 });