bolt put nil is del

bolt.go

@@ -60,6 +60,9 @@ func (b *Bolt) Set(key string, value []byte, ns ...string) error {
 		if err != nil {
 			return err
 		}
+		if value == nil {
+			return bkt.Delete(key)
+		}
 		return bkt.Put([]byte(key), value)
 	})
 }