Frontend: Fixed the null error in tooltips

fe_calckey/frontend/client/src/directives/tooltip.ts

@@ -118,6 +118,6 @@ export default {
     unmounted(el, binding, vn) {
         const self = el._tooltipDirective_;
         window.clearInterval(self.checkTimer);
-        self.close();
+        if (self) self.close();
     },
 } as Directive;