Again in the need of some hint.

I am exporting some subtree.

There is a custom_id pointing in the same org 

file but outside of the subtree.

* Foo

:PROPERTIES:

:CUSTOM_ID: foo

:END:

Lorem ipsum...

When I try to export the second subtree, I get

an error from #'org-export-resolve-id-link.

(user-error Unable to resolve link: "foo")

What is the easiest way to trap this error

so that I can compute something myself for this link ?

Thanks in advance.

Fabrice