Strange random error came through Kadira this morning

help
1 
TypeError: null is not an object (evaluating 'document.querySelector('title').textContent')

Error:
    at window.onerror (http://xyz.com/?gclid=xx:1:89)

We’ve got quite a few visitors coming in, but only one person got this error. How do I trace this?

2

It may be a browser plugin injecting some ad content which then barfs up that error probably.