PIV: When generating a key, command fails if --domain-component is not given

[sosthene-nitrokey]

I think likely an error add from: #582

$ nitropy nk3 piv --experimental generate-key --key 9A --algo rsa2048 --subject-name "VPN Test" --subject-alt-name-upn "vpntest-my.ad.test" --path vpntest.csr
Command line tool to interact with Nitrokey devices 0.7.3
Enter the PIN: 
Nitrokey Nitrokey 3 [CCID/ICCD Interface] 00 00
Critical error:
An unhandled exception occurred
	Exception encountered: ValueError('a relative distinguished name cannot be empty')

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Critical error occurred, exiting now
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