title: Office365 App for Excel Web: "Value cannot be null. Parameter name: conversationId"
body: <p>I have developed an Office 365 app using MEAN-JS - ie Express and Node.js. It runs fine on Excel Desktop environment, but when running on Excel's Web App environment I am getting this error while the app is loading into the frame:</p>
  
  <p>Sys.ArgumentNullException: Value cannot be null.
  Parameter name: conversationId</p>
  
  <p>File: excel-web-16.00.js, Line: 11, Column: 49669</p>
  
  <p>From what I can research conversationId should be part of the API for mail apps, not Excel apps. So I am not sure why the Excel-Web-16.00.js API is looking for this parameter?</p>
  
  <p>I've set up the test environment for Excel Web by loading the app manifest into an Office 365 Developer Sharepoint site, then running Excel Online and inserting the app.</p>
  
  <p>Has anyone come across this before?</p>
  
  <p>Thanks for your help.</p>