fix(timer): handle missing timer in isActive method

utils/TimerMgr.js

@@ -41,8 +41,12 @@ class TimerMgr {
         return this.#timers.hasOwnProperty(id);
     }
 
-    isActive(identifier) {
+    isActive(id) {
-        return this.#timers[identifier].isActive();
+        if (!this.hasTimer(id)) {
+            log.warn(`No timer with id ${id} found`);
+            return false;
+        }
+        return this.#timers[id].isActive();
     }
 
     cancelAll() {