Google Apps substring from null - google-apps-script

Question

I put my first Google Apps Script together to write emails to a spreadsheet. It works fine, except of the substring method I would like to use to shorten the message body. The script engine returns "cannot call substring from null […]". I found this thread (google apps script TypeError: Cannot call method "substring" of undefined) but the solution didn't help – or I didn't understand it which is about as likely.
Here's my script.
function labelToSpreadsheet() {
var threads = GmailApp.getUserLabelByName('newaddress').getThreads();
var spreadsheet = SpreadsheetApp.openById("onehellofanID")
var sheet = spreadsheet.getSheets()[0];
Logger.log (spreadsheet.getName());
for (var i = 0; i < threads.length; i++) {
var messages = threads[i].getMessages();
for (var j = 0; j < messages.length; j++) {
var shortendContent = messages[j].getPlainBody().substring(0, 500);
sheet.appendRow([messages[j].getSubject(), messages[j].getFrom(), messages[j].getReplyTo(), messages[j].getDate(), shortendContent]);
}
}
};

Answer 1

This was driving me nuts, as there was no reason your code wouldn't work, and I was getting the same error. I narrowed it down to the 'getPlainBody()' was returning 'null', but couldn't figure out why this was the case even when I used GMails own example.
I was almost going to call it a bug when I realized that what was happening was that some messages were returning nothing in the body. Specifically, some companies send out newsletters that aren't text content at all, but in fact are images with their content inside (Which was the case with the first message in the test label I had, thus driving me bonkers).
So, the issue here is that the label you're running this under has some messages where the content is only an image, no text whatsoever (Or potentially, is just completely blank), thus 'getPlainBody()' returns 'There's nothing there'(Null) and you can't get a substring of nothing.
A simple 'if' statement actually handles this error really well, as you can then tell the script to write to the sheet 'The content of this message was an image' (Or whatever you want).
This slightly modified version of your code works for me:
function labelToSpreadsheet() {
var threads = GmailApp.getUserLabelByName(LABELNAME).getThreads();
var spreadsheet = SpreadsheetApp.openById(SHEETID);
var sheet = spreadsheet.getSheets()[0];
for (var i = 0; i < threads.length; i++) {
var messages = threads[i].getMessages();
for (var j = 0; j < messages.length; j++) {
if(messages[j].getPlainBody() == null){
var shortendContent = 'This message was an image';
}else{
var shortendContent = messages[j].getPlainBody().substring(0, 500);
};
sheet.appendRow([messages[j].getSubject(), messages[j].getFrom(), messages[j].getReplyTo(), messages[j].getDate(), shortendContent]);
}
}
};
I'm giving myself a gold star for this one, it was annoying to figure out.