When used with caching, an empty value in metadata causes the following exception: CRITICAL: 'object' object is not iterable when the layer is set to reader. It doesn't seem to have the same problem with generator.
---
author: Joseph Reagle
category: praxis
date: '2013-12-02'
tags: ''
title: Archiving sources
...
Later this week I'll be participating on a panel of the [New Media in American Literary History Interdisciplinary Symposium](http://www.northeastern.edu/nulab/nmalh/). I plan to [talk](https://reagle.org/joseph/talks/2013/12-bib-bitrot.html) about bibliography and bitrot.
When used with caching, an empty value in metadata causes the following exception:
CRITICAL: 'object' object is not iterable
when the layer is set toreader
. It doesn't seem to have the same problem with generator.