Code Problem

Code Problem

Hi
I am a beginner with creator and I am following the tutorial - Add Business Logic  -  https://www.zoho.com/creator/help/tutorials/add-business-logic.html
In one exercise we are asked to enter this code. 
if (input.Products.size() > 3 && input.Products.size() <=5) 
My problem is that every time I enter it I get the message

Error at line number : 1  
Not able to find 'size' function

The size function comes from a built in Map Function.  Please can someone tell me how to get passed this problem.

Thank you