Require nonblank notification identities

internal/config/validate.go

@@ -152,6 +152,9 @@ func validateDistributorNotify(cfg DistributorNotifyConfig) error {
 	if _, err := RenderDistributorPipelineID(cfg.PipelineIDTemplate, values); err != nil {
 		return err
 	}
+	if _, err := RenderDistributorIdempotencyKey(cfg.IdempotencyKeyTemplate, values); err != nil {
+		return err
+	}
 	if err := validateDistributorBatchNotify(cfg.Batch); err != nil {
 		return err
 	}