setup nginx not to crash if host in proxy pass not found

Is your feature request related to a problem? Please describe.
When the proxy_host is used to proxy a docker container and this container is shut down afterwards, if you restart nginx-proxy-manager, it generates an error because the domain no longer exists. Nginx-proxy-manager can no longer launch.

Describe the solution you'd like
Modify the proxy pass option in nginx
actual :
proxy_pass http://:/;
proposal :

No stop when error on config

https://stackoverflow.com/questions/32845674/setup-nginx-not-to-crash-if-host-in-upstream-is-not-found/32846603#32846603

https://stackoverflow.com/questions/35744650/docker-network-nginx-resolver/37656784#37656784

resolver 127.0.0.11 valid=30s ipv6=off;
set $upstream_pass http://:/;
proxy_pass $upstream_pass;

Describe alternatives you've considered
Easier access to proxy_host configuration when nginx-proxy-manager is off to remove non-working configuration

Additional context
error when nginx-proxy-manager is restarted :
host not found in upstream "bar:3000" in /data/nginx/proxy_host/1.conf

Start by locating the code or template that generates /data/nginx/proxy_host/1.conf and inspect how proxy_pass is assembled. Reproduce a restart with an unavailable Docker hostname such as bar:3000, then verify that nginx starts and that a later-resolved container still proxies correctly. Done means an unavailable proxy host no longer prevents nginx-proxy-manager from launching.