What is the unexpected error in my code? - google-apps-script

Question

I am trying to create a calendar event in Google App Script, it is similar to the "QuickAdd" format that is used in the calendar. I used the createEventFromDescription method, I checked the execution transcript and it creates the event successfully but then the script shows an error when running the script.
The error message is "Error Encountered: An unexpected error occured"
I don't know what I have done wrong, it creates the event. Below is the code:
function doGet(){
var app = UiApp.createApplication().setTitle('QuickAdd Events');
//Create a penel which holds all the form elelemnts
var parent = app.createHorizontalPanel().setId('parent');
var left = app.createVerticalPanel().setId('left');
var right = app.createVerticalPanel().setId('right');
var eventTitleLabel = app.createLabel('Event Title:');
var eventTitle = app.createTextBox().setName('eventTitle');
var eventButton = app.createButton('Create Events');
var cancelButton = app.createButton('Cancel');
left.add(eventTitleLabel)
.add(eventTitle);
right.add(eventButton)
.add(cancelButton);
var eventHandler = app.createServerClickHandler('createEvents');
eventHandler.addCallbackElement(left);
//Add this handler to the button
eventButton.addClickHandler(eventHandler);
parent.add(left)
.add(right);
app.add(parent);
app.close();
return app;
}
function createEvents(e){
//Get the active application
var app = UiApp.getActiveApplication();
try{
//get the entries;
var event = e.parameter.eventTitle;
//Get the calendar
var cal = CalendarApp.getDefaultCalendar();
cal.createEventFromDescription(event);
app.add(app.createLabel('Event created Successfully'));
//make the form panel invisible
app.getElementById('panel').setVisible(false);
return app;
}
//If an error occurs, show it on the panel
catch(e){
app.add(app.createLabel('Error occured: '+e));
return app;
}
}

Answer 1

You are calling getElementById ('panel') but there is no widget called 'panel'... the closest is the panel called 'parent', is that the one you want to hide?