diff --git a/metric/metric.go b/metric/metric.go
index 23c48697f521d0bb1f7c1f221fc5973ee24ac02c..0af445c2d1f9e7a6d6e1b3c5d943fa519cfaf94a 100644
--- a/metric/metric.go
+++ b/metric/metric.go
@@ -247,11 +247,7 @@ func convertField(v interface{}) interface{} {
 	case int64:
 		return v
 	case string:
-		if v == "" {
-			return nil
-		} else {
-			return v
-		}
+		return v
 	case bool:
 		return v
 	case int: