Log no metrics found at debug level in cloudwatch input (#6665)

plugins/inputs/cloudwatch/cloudwatch.go

@@ -1,7 +1,6 @@
 package cloudwatch
 
 import (
-	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -12,7 +11,6 @@ import (
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/cloudwatch"
-
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/filter"
 	"github.com/influxdata/telegraf/internal"
@@ -44,6 +42,8 @@ type (
 		CacheTTL  internal.Duration `toml:"cache_ttl"`
 		RateLimit int               `toml:"ratelimit"`
 
+		Log telegraf.Logger `toml:"-"`
+
 		client          cloudwatchClient
 		statFilter      filter.Filter
 		metricCache     *metricCache
@@ -197,6 +197,10 @@ func (c *CloudWatch) Gather(acc telegraf.Accumulator) error {
 		return err
 	}
 
+	if len(queries) == 0 {
+		return nil
+	}
+
 	// Limit concurrency or we can easily exhaust user connection limit.
 	// See cloudwatch API request limits:
 	// http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_limits.html
@@ -481,7 +485,8 @@ func (c *CloudWatch) getDataQueries(filteredMetrics []filteredMetric) ([]*cloudw
 	}
 
 	if len(dataQueries) == 0 {
-		return nil, errors.New("no metrics found to collect")
+		c.Log.Debug("no metrics found to collect")
+		return nil, nil
 	}
 
 	if c.metricCache == nil {