{
  # concat with null argument data expression
  # empty configs are not accepted by Kea
  "Dhcp4": {
    "valid-lifetime": 1800,
    "client-classes": [
      # null left argument
      /// match: concat('', suffix(option dhcp.host-name, 3))
      {
        "name": "null-left"
      },
      /// subclass selector 'com'
      {
        "name": "sub#null-left#0",
        /// from: match concat('', suffix(option dhcp.host-name, 3))
        /// data: 'com'
        "test": "substring(option[12].hex,-3,all) == 'com'"
      },
      # null right argument
      /// match: concat(suffix(option dhcp.host-name, 3), substring('foobar', 0, 0))
      {
        "name": "null-right"
      },
      /// subclass selector 'org'
      {
        "name": "sub#null-right#1",
        /// from: match concat(suffix(option dhcp.host-name, 3), substring('foobar', 0, 0))
        /// data: 'org'
        "test": "substring(option[12].hex,-3,all) == 'org'"
      }
    ]
  }
}