Comment 5 for bug 1841105

The attached base bundle defines the following set of variables:

# Variables
debug: &debug True
verbose: &verbose True
openstack_origin: &openstack_origin cloud:bionic-rocky
source: &source cloud:bionic-rocky
num_compute_units: &num_compute_units 1

ssl_ca: &ssl_ca
ssl_cert: &ssl_cert
ssl_key: &ssl_key

The ssl_* ones (which are defined to null in the above snippet) are referenced in the nova-cloud-controller app from the base bundle:

 nova-cloud-controller:
    num_units: 1
    charm: cs:~openstack-charmers-next/nova-cloud-controller
    constraints: mem=2G
    options:
      debug: *debug
      verbose: *verbose
      network-manager: Neutron
      openstack-origin: *openstack_origin
      ssl_ca: *ssl_ca
      ssl_cert: *ssl_cert
      ssl_key: *ssl_key

This causes a nil value to be passed into "visitField" which triggers the panic. Adding a check for nil values in the top of that function resolves the issue. I will push a PR with a fix.