Experiments with "" (empty strings) and <null> do not reproduce this:
sqlite> SELECT * FROM items_generic; _id|created|modified|subtype|name|text|image 1|1297375866315|1297375868395|/items/generic|A|A|2130837526 2|1297375548767|1297375548767|/items/generic|||2130837526 -> empty 3|1297376458397|1297376463616|/items/generic|C|C|2130837526 4|1297375548767|1297375548767|/items/generic|||2130837526 -> null
Experiments with "" (empty strings) and <null> do not reproduce this:
sqlite> SELECT * FROM items_generic; modified| subtype| name|text| image |1297375868395| /items/ generic| A|A|2130837526 |1297375548767| /items/ generic| ||2130837526 -> empty |1297376463616| /items/ generic| C|C|2130837526 |1297375548767| /items/ generic| ||2130837526 -> null
_id|created|
1|1297375866315
2|1297375548767
3|1297376458397
4|1297375548767