Cannot read property 'getMonth' of null

Thanks for posting in the Community, @saraycarpeton.

We are very concerned when there's an unexpected behavior in QuickBooks Online. I'll make sure that you can rid of that error.

Let me share with you a few things you can do whenever you get these types of error messages in QuickBooks Online (QBO). But before that, you can also try refreshing your QuickBooks page, logging out and logging back in, or even restarting your computer.

First, I'd like to start off by doing some troubleshooting to determine if this isn't a browser-related issue. When was the last time you cleared cache and cookies on your browser? Doing this will help fix most issues the site may be having. Here's an article that shows you how to do that: How to clear Cache and Cookies. 

If non of the initial steps works, you'll want to sign in to QuickBooks using a private browser. This disables its extensions and stops the cache from saving your browsing history.

• Google Chrome: Ctrl + Shift + N
• MS Edge and Firefox: Ctrl + Shift + P
• Safari: Command + Shift + N

If nothing works, please contact our Support team to check this further. They can start a screen-sharing session to gather more details about this error.

Tag me in a comment below if you have other questions about error messages in QBO. I'll be sure to get back to you. Have a great day!