Ensuring that we are not emitting stats when handle is nil (#1723)

* Ensuring that we are not emitting stats when handle is nil

* Updated the changelog

CHANGELOG.md

@@ -12,6 +12,8 @@ BUG FIXES:
   * client: Prevent race when persisting state file [GH-1682]
   * client: Artifact download failures will be retried before failing tasks
     [GH-1558]
+  * client: Fix a crash related to stats publishing when driver hasn't started
+    yet [GH-1723]
   * client/fingerprint: Fix inconsistent CPU MHz fingerprinting [GH-1366]
   * discovery: Fix old services not getting removed from consul on update
     [GH-1668]

client/task_runner.go

@@ -502,8 +502,11 @@ func (r *TaskRunner) collectResourceUsageStats(stopCollection <-chan struct{}) {
 	for {
 		select {
 		case <-next.C:
-			ru, err := r.handle.Stats()
 			next.Reset(r.config.StatsCollectionInterval)
+			if r.handle == nil {
+				continue
+			}
+			ru, err := r.handle.Stats()
 
 			if err != nil {
 				// We do not log when the plugin is shutdown as this is simply a