Cannot read property 'onOpen' of null

This error message typically indicates that the code is attempting to access a property or method of an object that is null, meaning it does not exist or has not been initialized.

In this case, it seems that there is an issue with the code related to the onOpen trigger. The onOpen trigger is a reserved function in Google Apps Script that is automatically called when a user opens a spreadsheet or document.

To resolve this error, you should check that the code is properly accessing the spreadsheet or document, and that any necessary libraries or dependencies have been properly initialized. You may also need to check that the correct function name has been used for the onOpen trigger.

If you are unsure how to fix the issue, you can try searching for similar issues online or reaching out to the Google Apps Script community for assistance.