atc: avoid nil dereference in prometheus metric
fixes
@@ -303,6 +303,7 @@ func (config *PrometheusConfig) NewEmitter() (metric.Emitter, error) {
schedulingLoadingDuration: schedulingLoadingDuration,
workerContainers: workerContainers,
+ workersRegistered: workersRegistered,
workerLastSeen: map[string]time.Time{},
workerVolumes: workerVolumes,
}
