Cryptic error message if one of the secrets values is an integer and not a string

[kutu-dev]

Having a YAML file like:

userPassword: 1234

Will fail with the error:

/nix/store/vxv8vsvf4vghkncqdnwgjhknzddxqy6q-sops-install-secrets-0.0.1/bin/sops-install-secrets: secret userPassword in /nix/store/29756kkx2w1z2m21abbwgvi1ad8b2lnb-data.enc.yaml is not valid: the value of key '' is not a string

Instead of printing the key name userPassword it just reports an empty key making things more confusing.