Fix panic on docker healthcheck collection (#9171) (#9181)

Fix panic on docker healthcheck collection on dockers without healthchecks.

(cherry picked from commit 1c43d6c)

CHANGELOG.asciidoc

@@ -45,6 +45,7 @@ https://github.com/elastic/beats/compare/v6.5.1...6.5[Check the HEAD diff]
 
 *Metricbeat*
 
+- Fix panic on docker healthcheck collection on dockers without healthchecks. {pull}9171[9171]
 - Fix issue preventing diskio metrics collection for idle disks. {issue}9124[9124] {pull}9125[9125]
 
 *Packetbeat*

metricbeat/module/docker/healthcheck/data.go

@@ -50,6 +50,12 @@ func eventMapping(cont *types.Container, m *MetricSet) common.MapStr {
 		logp.Err("Error inspecting container %v: %v", cont.ID, err)
 		return nil
 	}
+
+	// Check if the container has any health check
+	if container.State.Health == nil {
+		return nil
+	}
+
 	lastEvent := len(container.State.Health.Log) - 1
 
 	// Checks if a healthcheck already happened