title: how to debug angular error with no information
body: <p>I get an error `ERROR Error: "[object Object]" in my console and my app just has a white screen. It was working fine, and I can't think what I've changed if anything. It shows as being in core.js not my code so how can I debug this?</p>
  
  <p>My app is Angular version 7. Along time ago it was version 2, but has been upgraded over time. </p>
  
  <p><a href="https://i.stack.imgur.com/RkmjH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RkmjH.png" alt="enter image description here"></a></p>