diff --git a/frontend/__mocks__/localStorage.ts b/frontend/__mocks__/localStorage.ts
index e920671557d..c727e8312f0 100644
--- a/frontend/__mocks__/localStorage.ts
+++ b/frontend/__mocks__/localStorage.ts
@@ -1,11 +1,11 @@
 let _localStorage = {};
 
 (window as any).localStorage = (window as any).sessionStorage = {
-  setItem(key, value) {
+  setItem(key: string, value: string) {
     Object.assign(_localStorage, { [key]: value} );
   },
-  getItem(key) {
-    return _localStorage[key] || null;
+  getItem(key: string): string | null {
+    return _localStorage.hasOwnProperty(key) ? _localStorage[key] : null;
   },
   clear() {
     _localStorage = {};