home_domain error

I'm getting this error in the validator:
![picture](https://user-images.githubusercontent.com/26092447/95470374-18559a00-0957-11eb-9532-fec74a2eec58.png)

I couldn't find documentation regarding that `home_domain` field. It isn't mentioned in [SEP-1](https://github.com/stellar/stellar-protocol/blob/master/ecosystem/sep-0001.md).