return error on unsupported serializer data format (#2542)

CHANGELOG.md

@@ -81,6 +81,7 @@ be deprecated eventually.
 - [#2500](https://github.com/influxdata/telegraf/pull/2500): Remove warning if parse empty content
 - [#2520](https://github.com/influxdata/telegraf/pull/2520): Update default value for Cloudwatch rate limit
 - [#2513](https://github.com/influxdata/telegraf/issues/2513): create /etc/telegraf/telegraf.d directory in tarball.
+- [#2541](https://github.com/influxdata/telegraf/issues/2541): Return error on unsupported serializer data format.
 
 ## v1.2.1 [2017-02-01]
 

plugins/serializers/registry.go

 package serializers
 
 import (
+	"fmt"
+
 	"github.com/influxdata/telegraf"
 
 	"github.com/influxdata/telegraf/plugins/serializers/graphite"
@@ -49,6 +51,8 @@ func NewSerializer(config *Config) (Serializer, error) {
 		serializer, err = NewGraphiteSerializer(config.Prefix, config.Template)
 	case "json":
 		serializer, err = NewJsonSerializer()
+	default:
+		err = fmt.Errorf("Invalid data format: %s", config.DataFormat)
 	}
 	return serializer, err
 }