How to debug empty unhandled promise rejection?

[christianinsert]

In a test spec, I keep getting:

CypressError: The following error originated from your application code, not from Cypress. It was caused by an unhandled promise rejection.

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When Cypress detects uncaught errors originating from your application it will automatically fail the current test. 

Yes, the error message is empty.
In the corresponding video, it says (uncaught exception) undefined: undefined - which is not very helpful either.

How can I debug such cases?
I have found out so far that it never happens when running in graphical mode. Whereas in head-less mode it fails always in Electron, but only sometimes in Chrome. But still, without a proper error message, that doesn't help much.

[pompan129]

One suggestion that helped me was to add

Cypress.on("uncaught:exception", (err, runnable) => {
console.log("uncaught:exception",err);
  return false;
});

at the top of a failing test (above describe()). I was able to see the stack trace then and debug from there.