HostnameOrIPv4AddressOrEmptyString (type)

{
  "id": "HostnameOrIPv4AddressOrEmptyString", 
  "maxLength": 255, 
  "module_id": "Common", 
  "pattern": "^(?=.{1,255}$)[0-9A-Za-z](?:(?:[0-9A-Za-z]|-){0,61}[0-9A-Za-z])?(?:\\.[0-9A-Za-z](?:(?:[0-9A-Za-z]|-){0,61}[0-9A-Za-z])?)*\\.?$|^$", 
  "title": "Hostname or IPv4 address", 
  "type": "string"
}