You don't need a valid FQDN inside private Lan networks.

E.g. because we have everything locally available and locked out from the outside our Jenkins address is "jenkins" and it is perfectly valid for Bitbucket server API. 

You are checking for the existence of a . (dot) to verify the URL and it is breaking our process since it isn't publishing the build status.

The following error appears:

Can not determine Jenkins root URL or Jenkins URL is not a valid URL regarding Bitbucket API. Commit status notifications are disabled until a root URL is configured in Jenkins global configuration.

We traced down the error and created our own version of the plugin editing the method "checkURL" from the BitbucketBuildStatusNotifications.java file which does not make the dot check and it works perfectly.

Please take a look at this as it is blocking us from future updates of this plugin.