return early for nil target groups

discovery/manager.go

@@ -154,7 +154,11 @@ func (m *Manager) updateGroup(poolKey poolKey, tgs []*targetgroup.Group) {
 	done := make(chan struct{})
 
 	m.actionCh <- func(ctx context.Context) {
-		if tgs != nil {
+		if tgs == nil {
+			close(done)
+			return
+		}
+
 		for _, tg := range tgs {
 			if tg != nil { // Some Discoverers send nil targetgroup so need to check for it to avoid panics.
 				if _, ok := m.targets[poolKey]; !ok {
@@ -163,7 +167,6 @@ func (m *Manager) updateGroup(poolKey poolKey, tgs []*targetgroup.Group) {
 				m.targets[poolKey][tg.Source] = tg
 			}
 		}
-		}
 		close(done)
 
 	}