To reproduce:
```
set pki certificate repka acme domain foo.bar.com
set pki certificate repka acme email 'someone@gmail.com'
set pki certificate repka acme url https://acme-staging-v02.api.letsencrypt.org/directory
```
```
vyos@-VFW046# commit
[ pki ]
Updating configuration: "vpn ipsec remote-access connection rw
authentication x509 certificate repka"
Traceback (most recent call last):
File "/usr/libexec/vyos/services/vyos-configd", line 145, in run_script
script.verify(c)
File "/usr/libexec/vyos//conf_mode/pki.py", line 381, in verify
certbot_request(name, cert_conf['acme'])
File "/usr/libexec/vyos//conf_mode/pki.py", line 147, in certbot_request
if ('haproxy' in dict_search('used_by', config) and
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: argument of type 'NoneType' is not iterable
[[pki]] failed
Commit failed
```