"Error Encountered: Invalid Argument" in handler function - google-apps-script

Question

I'm getting this error in my handler function but I've no clue what's causing it. I've copied the code and debugged it in a non-handler function and there was no error.
function _responseToNext(e) {
var app = UiApp.getActiveApplication();
app.getElementById('btnPrev').setEnabled(true);
var current = parseInt(CacheService.getPublicCache().get('currentItem'));
var agendaItems = Utilities.jsonParse(CacheService.getPublicCache().get('agenda'));
agendaItems[current]['notes'] = e.parameter.tAreaNotes;
agendaItems[current]['status'] = e.parameter.lboxStatus;
CacheService.getPublicCache().put('agenda', Utilities.jsonStringify(agendaItems));
current = current + 1;
CacheService.getPublicCache().put('currentItem', current);
fillAgendaDetail(app);
// only enabled 'Next' if there are more items in the agenda
if (current < agendaItems.length-1) {
app.getElementById('btnNext').setEnabled(true);
}
return app;
}

Answer 1

I suppose, the error cause is that the Cache get method returns null during the 1st execution when the cache is empty. The Utilities.jsonParse throws an exception and the cache becomes in any case empty. Try to use the following modified code.
function _responseToNext(e) {
var app = UiApp.getActiveApplication();
app.getElementById('btnPrev').setEnabled(true);
var cachedCurrent = CacheService.getPublicCache().get('currentItem');
var current;
if (cachedCurrent == null) {
current = 0;
}
else {
current = parseInt(cachedCurrent);
}
var cachedAgendaItems = CacheService.getPublicCache().get('agenda');
var agendaItems;
if (cachedAgendaItems == null) {
agendaItems = [][];
}
else {
agendaItems = Utilities.jsonParse();
}
agendaItems[current]['notes'] = e.parameter.tAreaNotes;
agendaItems[current]['status'] = e.parameter.lboxStatus;
CacheService.getPublicCache().put('agenda', Utilities.jsonStringify(agendaItems));
current = current + 1;
CacheService.getPublicCache().put('currentItem', current);
fillAgendaDetail(app);
// only enabled 'Next' if there are more items in the agenda
if (current < agendaItems.length-1) {
app.getElementById('btnNext').setEnabled(true);
}
return app;
}
Also please mention that the Public Cache (CacheService.getPublicCache()) is the same for all users of your script. In your case, this means, if two users user1#example.com and user2#example.com use the script they will have the same current and agendaItems variables values, i.e. it can be a situation when the _responseToNext handler is already executed under the user1 authority - the current variable is equal to 1, after the user2 executes the _responseToNext handler - the current variable is equal to 2 and so on. If you do not need such behaviour, use the CacheService.getPrivateCache().