private Set<String> validateGracePeriodAndExternalPorts(final Job job) { final Integer gracePeriod = job.getGracePeriod(); if (gracePeriod != null && gracePeriod > 0 && job.hasExternalPorts()) { return singleton("Job has both grace period and static/external ports. External ports will " + "prevent new containers from deploying during the gracePeriod because of port " + "conflicts. Please choose one or the other."); } return emptySet(); }