Unable to connect: Firefox can’t establish a connection to the server at 192.168.1.39:8123

Installation
16

I tried connecting a screen, but the boot process showed no errors.
I did a ha core check and it showed some errors:

~ $ ha core check
Processing... Done.

Error: Testing configuration at /config
INFO:homeassistant.helpers.storage:Migrating core.device_registry storage from 1.2 to 1.3
INFO:homeassistant.helpers.storage:Migrating core.entity_registry storage from 1.4 to 1.7
Fatal error while loading config: 'null' is not a valid RegistryEntryDisabler
Failed config
  General Errors: 
    - 'null' is not a valid RegistryEntryDisabler

Successful config (partial)

I’ll have a look at the core config files, but tread very carefully!
Jim