cfssl gencert fails on generation from json (v 1.2)

[cfssl][1] v 1.2

cfssl gencert -initca ca/ca-csr.json

where the json is:

{
"hosts": [
"cluster.local"
],
"key": {
"algo": "rsa",
"size": 2048
},
"names": [
{
"C": "CA",
"L": "Montreal",
"O": "My Inc.",
"OU": "QC",
"ST": "Montreal"
}
]
}

I got a err msg:
> Must specify bundle target through -cert or -domain

From the [example][2] seems I use it the same way.

checking the [code][3]:

not sure how would it go to that condition.

Q: what actually the way I can use it? to generate the certificate from the JSON file.

[1]: https://pkg.cfssl.org/
[2]: https://scriptcrunch.com/create-ca-tls-ssl-certificates-keys/
[3]: https://github.com/cloudflare/cfssl/blob/master/cli/bundle/bundle.go