fix https://github.com/chrislusf/seaweedfs/issues/2452
@ -226,7 +226,7 @@ func writeToFile(client volume_server_pb.VolumeServer_CopyFileClient, fileName s
if receiveErr == io.EOF {
break
}
if resp.ModifiedTsNs != 0 {
if resp!=nil && resp.ModifiedTsNs != 0 {
modifiedTsNs = resp.ModifiedTsNs
if receiveErr != nil {