{
  # pick-first-value data expression
  # empty configs are not accepted by Kea
  "Dhcp6": {
    "valid-lifetime": 1800,
    "client-classes": [
      # reduce literals
      {
        "name": "literal",
        /// from: match if (option dhcp6.client-data) = (pick-first-value(substring('abcd', 0, 0), null, 'foobar'))
        "test": "option[45].hex == 'foobar'"
      },
      # null
      {
        "name": "null",
        /// from: match if (option dhcp6.client-data) = (pick-first-value(null))
        "test": "option[45].hex == ''"
      }
    ]
  }
}