flexible option hook is calculating v6 domain names length incorrectly

Test case is very simple, configuration as follows:

{
    "Dhcp6": {
        "hooks-libraries": [
            {
                "library": "/home/wlodek/installed/git-thread/lib/kea/hooks/libdhcp_flex_option.so", 
                "parameters": {
                    "options": [
                        {
                            "code": 30, 
                            "supersede": "ifelse(relay6[0].peeraddr == 3000::1005, 'ntp.example.com','')"
                        }
                    ]
                }
            }
        ], 
        "interfaces-config": {
            "interfaces": [
                "enp0s9"
            ]
        }, 
        "lease-database": {
            "type": "memfile"
        }, 
        "loggers": [
            {
                "debuglevel": 99, 
                "name": "kea-dhcp6", 
                "output_options": [
                    {
                        "output": "/home/wlodek/installed/git-thread/var/log/kea.log"
                    }
                ], 
                "severity": "DEBUG"
            }
        ], 
        "multi-threading": {
            "enable-multi-threading": true, 
            "packet-queue-size": 16, 
            "thread-pool-size": 2
        }, 
        "option-data": [
            {
                "code": 30, 
                "csv-format": true, 
                "data": "ntp.example.com", 
                "name": "nisp-domain-name", 
                "space": "dhcp6"
            }
        ], 
        "preferred-lifetime": 3000, 
        "rebind-timer": 2000, 
        "renew-timer": 1000, 
        "shared-networks": [], 
        "subnet6": [
            {
                "interface": "enp0s9", 
                "pools": [
                    {
                        "pool": "2001:db8:1::1-2001:db8:1::1"
                    }
                ], 
                "subnet": "2001:db8:1::/64"
            }
        ], 
        "valid-lifetime": 4000
    }
}

We have configured option "nisp-domain-name" at global level and in flexible option, with the same value!

And I'm sending two advertise (inside Relay Forward), one message has peeraddr == 3000::1005 other don't. Kea is configured in a way that those two reply messages should be identical, but one of those will have "nisp-domain-name" option added by Kea core, other will have "nisp-domain-name" added by hook.

capture.pcap

Result is that hook is adding option with incorrect length calculated. Used forge to find it. attaching capture from test.

logs looks correct

2020-08-06 01:03:46.128 DEBUG [kea-dhcp6.callouts/29307.140183868143360] HOOKS_CALLOUTS_BEGIN begin all callouts for hook pkt6_send
2020-08-06 01:03:46.129 DEBUG [kea-dhcp6.eval/29307.140183868143360] EVAL_DEBUG_RELAY6 Pushing PKT6 relay field peeraddr nest 0 with value 0x30000000000000000000000000001005
2020-08-06 01:03:46.129 DEBUG [kea-dhcp6.eval/29307.140183868143360] EVAL_DEBUG_IPADDRESS Pushing IPAddress 0x30000000000000000000000000001005
2020-08-06 01:03:46.129 DEBUG [kea-dhcp6.eval/29307.140183868143360] EVAL_DEBUG_EQUAL Popping 0x30000000000000000000000000001005 and 0x30000000000000000000000000001005 pushing result 'true'
2020-08-06 01:03:46.129 DEBUG [kea-dhcp6.eval/29307.140183868143360] EVAL_DEBUG_STRING Pushing text string 'ntp.example.com'
2020-08-06 01:03:46.129 DEBUG [kea-dhcp6.eval/29307.140183868143360] EVAL_DEBUG_STRING Pushing text string ''
2020-08-06 01:03:46.129 DEBUG [kea-dhcp6.eval/29307.140183868143360] EVAL_DEBUG_IFELSE_TRUE Popping 'true' (true) and 0x, leaving 0x6E74702E6578616D706C652E636F6D
2020-08-06 01:03:46.130 DEBUG [kea-dhcp6.flex-option-hooks/29307.140183868143360] FLEX_OPTION_PROCESS_SUPERSEDE Supersedes the value of option code 30 by 'ntp.example.com'
2020-08-06 01:03:46.130 DEBUG [kea-dhcp6.callouts/29307.140183868143360] HOOKS_CALLOUT_CALLED hooks library with index 1 has called a callout on hook pkt6_send that has address 0x7f7f1b41ff30 (callout duration: 1.504 ms)