Dex set to null probably shouldn't throw a config error in update_ood_portal

[dev-sda1]

We just updated our Prod instance of Open OnDemand to 4.1 and temporarily encountered an issue that had us stumped for a few minutes, where ood-portal-generator was throwing You do not have dex installed, but are trying to configure it. Please install ondemand-dex or remove the configurations to continue. despite us not using Dex (we authenticate via MS365 OIDC).

We were able to get around this by removing dex: null from our ood_portal.yml, but ideally if it's set to null it should be ignored entirely? I see this behaviour was changed for 4.1 in #1994 but this seems to have been done with the assumption of a user trying to fully configure dex, which is fair enough, but this might cause some confusion as the config file does say If the value for "dex" key is false or null, Dex support is disabled

[johrstrom]

OK thanks the feedback, I think this could be better for sure.