'Send link' functionality auto testing. How to close Desktop Outlook window that is opened by click in tested web app?

Hello!

Please help to test ‘Send link’ functionality.

The Desktop Outlook window is opened by click on element in web app.
I need to close Outlook window, confirm no changes pop up and continue to interact with wab app.

I receive fail for Windows.closeApplication() keyword execution Caused by: java.lang.NullPointerException

Thank you in advance for your advice!