vendor-encapsulated-options in client-classes

Kea does not return vendor-encapsulated-options correctly when it is redefined in a client class. The following example is accepted by Kea:

"client-classes": [ {
    "name": "Test_One",
       "option-def": [ {
             "name": "vendor-encapsulated-options",
             "code":43,    
             "type": "string" } ],
       "option-data": [  {
             "name": "vendor-class-identifier",
             "csv-format":true, 
             "data": "Test" },  {
             "name": "vendor-encapsulated-options",
             "csv-format":true, 
             "data": "1.2.3.4" } ] } ],

But config-write returns the an empty data value, which is not accepted by Kea:

    "client-classes": [
        {
          "boot-file-name": "",
          "name": "Test_One",
          "next-server": "0.0.0.0",
          "option-data": [
            {
              "always-send": false,
              "code": 60,
              "csv-format": true,
              "data": "Test",
              "name": "vendor-class-identifier",
              "never-send": false,
              "space": "dhcp4"
            },
            {
              "always-send": false,
              "code": 43,
              "csv-format": true,
              "data": "",
              "name": "vendor-encapsulated-options",
              "never-send": false,
              "space": "dhcp4"
            }
          ],
          "option-def": [
            {
              "array": false,
              "code": 43,
              "encapsulate": "",
              "name": "vendor-encapsulated-options",
              "record-types": "",
              "space": "dhcp4",
              "type": "string"
            }
          ],
          "server-hostname": ""
        }
      ],

RT 23961

This behaviour first appears in Kea 2.5.3

Related to Kea ticket #3510 (closed)