fix(timer): handle missing timer in isActive method

utils/TimerMgr.js

@@ -10,6 +10,10 @@ class TimerMgr {
     }
 
     create(id, timeout, func) {
+        if (this.hasTimer(id)) {
+            log.error(`Timer with id ${id} already exists`);
+            return;
+        }
         log.debug("Create timer with id " + id);
         this.#timers[id] = actions.ScriptExecution.createTimer(id, timeout, func);
     }
@@ -37,8 +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() {