Make sure we omit the Kind value in JSON if empty

agent/structs/service_definition.go

@@ -14,7 +14,7 @@ import (
 // ServiceDefinition is used to JSON decode the Service definitions. For
 // documentation on specific fields see NodeService which is better documented.
 type ServiceDefinition struct {
-	Kind              ServiceKind
+	Kind              ServiceKind `json:",omitempty"`
 	ID                string
 	Name              string
 	Tags              []string

agent/structs/structs.go

@@ -512,7 +512,7 @@ type NodeService struct {
 	// Kind is the kind of service this is. Different kinds of services may
 	// have differing validation, DNS behavior, etc. An empty kind will default
 	// to the Default kind. See ServiceKind for the full list of kinds.
-	Kind ServiceKind
+	Kind ServiceKind `json:",omitempty"`
 
 	ID                string
 	Service           string