Avoid process crash when elasticsearch response is nil

Add nil pointer check in elasticsearch bulkprocessor's
after callback, defined inside pkg/es/config/config.go.
In some rare cases, elasticsearch request will return
error with nil response, and then nil response will
be passed into after callback, and using of nil pointer
will cause process crash.

Signed-off-by: Li Zhaoxing <lizhaoxing@4paradigm.com>

pkg/es/config/config.go

@@ -114,7 +114,7 @@ func (c *Configuration) NewClient(logger *zap.Logger, metricsFactory metrics.Fac
 			m.Delete(id)
 
 			// log individual errors, note that err might be false and these errors still present
-			if response.Errors {
+			if response != nil && response.Errors {
 				for _, it := range response.Items {
 					for key, val := range it {
 						if val.Error != nil {
@@ -127,13 +127,21 @@ func (c *Configuration) NewClient(logger *zap.Logger, metricsFactory metrics.Fac
 
 			sm.Emit(err, time.Since(start.(time.Time)))
 			if err != nil {
-				failed := len(response.Failed())
+				var failed int
+				var respval interface{}
+				if response == nil {
+					failed = 0
+					respval = "nil"
+				} else {
+					failed = len(response.Failed())
+					respval = response
+				}
 				total := len(requests)
 				logger.Error("Elasticsearch could not process bulk request",
 					zap.Int("request_count", total),
 					zap.Int("failed_count", failed),
 					zap.Error(err),
-					zap.Any("response", response))
+					zap.Any("response", respval))
 			}
 		}).
 		BulkSize(c.BulkSize).