Snapcraft build snap kernel fails with certificate error

I tried to build a snap kernel using The kernel plugin. I also used the Ubuntu focal snapcraft.yaml wih some changes, such as grade, sources…

The build fails with :

make[1]: *** No rule to make target 'debian/canonical-certs.pem', needed by 'certs/x509_certificate_list'.  Stop.
make: *** [Makefile:1809: certs] Error 2

I have read many posts suggested to override

CONFIG_SYSTEM_TRUSTED_KEYS="debian/canonical-certs.pem" 
CONFIG_SYSTEM_REVOCATION_KEYS="debian/canonical-revoked-certs.pem"

to

CONFIG_SYSTEM_TRUSTED_KEYS=""
CONFIG_SYSTEM_REVOCATION_KEYS=""

No success

Anyone has an idea ?