handleSerialError fails when setting err.routerCode with TypeError(s)
Fetch network requests or other fetch errors that don't even bring a response are automatically TypeError, and that object can't be extended, causing: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cant_define_property_object_not_extensible
MDN Web Docs
The JavaScript exception "can't define property "x": "obj" is not extensible" occurs
when Object.preventExtensions() marked an object as no longer extensible,
so that it will never have properties beyond the ones it had at the time it was marked
as non-extensible.
when Object.preventExtensions() marked an object as no longer extensible,
so that it will never have properties beyond the ones it had at the time it was marked
as non-extensible.
