Function is_secret 

pub fn is_secret(name: &str) -> bool

Names that must never be inside a backup.

A backup carries the log, the policy and the git objects. It does not carry the node’s key or anybody’s credential, and one that does is a copy of the node’s identity sitting on whatever disk the backup lives on. Fatal rather than a warning for that reason: the fix is to remove it and re-take the backup, not to note it.