iam group error handling (guest accounts)

I've created a guest account ens2ll

shock@RA:~$ iam guest new -f Eugenio -l Ns2lli -m test@delizio.so -d "Authorized Leonhard Med guest" -h eunaselli -a "ID SIS" -n t -c leomed-support@id.ethz.ch
{
    "admingroup": null,
    "birth_date": null,
    "category": "IAM-Gast",
    "cre_date": "2024-01-25T13:33:53",
    "department": null,
    "description": "Authorized Leonhard Med guest",
    "displayname": "Ns2lli Eugenio",
    "end_date": "2025-01-24",
    "firstname": "Eugenio",
    "gender": null,
    "gidNumber": "504775",
    "host_admingroup": "ID SIS",
    "host_leitzahl": "06007",
    "host_username": "eunaselli",
    "lastname": "Ns2lli",
    "leitzahl": null,
    "mail": "test@delizio.so",
    "mod_date": "2024-01-25T13:33:53",
    "notification": "To technical contact",
    "npid": "4067569",
    "nuid": "6133589",
    "orcid": null,
    "persid": null,
    "start_date": "2024-01-25",
    "state": "ENABLED",
    "technical_contact": "leomed-support@id.ethz.ch",
    "title": null,
    "type": "IAM-Identit\u00e4t",
    "uidNumber": "627403",
    "username": "ens2ll"
}

Added the service AD

shock@RA:~$ iam user ens2ll -g AD
{
    "services": [
        {
            "Assigned by": "",
            "delete_after": "24-JAN-2025",
            "enabled": "1",
            "login_until": "24-JAN-2025",
            "name": "LDAP"
        },
        {
            "Assigned by": "",
            "delete_after": "24-JAN-2025",
            "enabled": "1",
            "login_until": "24-JAN-2025",
            "name": "WLAN_VPN"
        },
        {
            "Assigned by": "manual",
            "delete_after": "24-JAN-2025",
            "enabled": "1",
            "login_until": "24-JAN-2025",
            "name": "Active Directory"
        }
    ]
}

When trying to add it to ID-LEOMED-SISRP I get:

shock@RA:~$ iam group ID-LEOMED-SISRP -a ens2ll
Traceback (most recent call last):
  File "/home/shock/.local/bin/iam", line 8, in <module>
    sys.exit(cli())
  File "/usr/lib/python3/dist-packages/click/core.py", line 1128, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 1053, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python3/dist-packages/click/core.py", line 1659, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python3/dist-packages/click/core.py", line 1395, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python3/dist-packages/click/core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/decorators.py", line 84, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "/home/shock/.local/lib/python3.10/site-packages/ethz_iam_webservice/main.py", line 468, in manage_group
    group.add_members(users=add, subgroups=add_subgroup)
  File "/home/shock/.local/lib/python3.10/site-packages/ethz_iam_webservice/group.py", line 267, in add_members
    group = self.new_from_data(data)
  File "/home/shock/.local/lib/python3.10/site-packages/ethz_iam_webservice/group.py", line 118, in new_from_data
    if data.get("certificationDate")
AttributeError: 'NoneType' object has no attribute 'get'

It gives the impression that the user hasn't been added because the get failed, when in reality:

shock@RA:~$ iam group ID-LEOMED-SISRP
{
    "admingroup": "ID SIS",
    "category": "Custom",
    "certification_date": "",
    "certification_note": "LeoMed",
    "certification_period": "No recertification",
    "cre_date": "2021-09-17T13:56:25",
    "description": "Access group for LeoMed 2.0",
    "gidNumber": "459479",
    "grid": "6087834",
    "group_ad_ou": "ou=Custom,ou=EthLists",
    "managers": [],
    "members": [
        "adm-lbrechbuehl",
        "barillac",
        "michalo",
        "strpeter",
        "ttestguestla",
        "rkuzyakiv",
        "ens2ll",
        "lbrechbuehl",
        "tguestlastna",
        "ID-SIS-RP-LMT"
    ],
    "mod_date": "2024-01-25T12:35:39",
    "name": "ID-LEOMED-SISRP",
    "state": "PROCESSED",
    "targets": [
        "AD",
        "LDAP"
    ]
}