How to avoid nginx failure in case of bad certificate ?

[Pierre Couderc]

In case of bad certificate (certificate file missing for exemple), nginx 
fails to restart.

Is there a way to avoid that ?

There may be an error on one site without stopping all other correct sites.

This occurs particularly in case we remove an old site, and make an 
error in configuration files : a few months later, let's encrypt tries 
to renew the certificate in the night and fails, then restarts nginx 
which fails because missing a no more used certificate, and the full 
site is stoped....

Thanks.

PC