private ApplicationVersions applicationVersions(ApplicationId applicationId) {
        ApplicationVersions versions = requestHandlers.get(applicationId);
        if (versions == null) throw new NotFoundException("No such application id: " + applicationId);

        return versions;
    }
Used during config request handling to route to the right config model
based on application id and version.

@author Vegard Sjonfjell
configserver/src/main/java/com/yahoo/vespa/config/server/application/ApplicationMapper.java