Reference

exp date isn't null, but text field is

1. Weekly epidemiological record (WER) No. 47, 2007, 82, 409–416.
2. Geographical distribution of Chikungunya cases 2001-2007 (data are presented as reporting period followed by estimated number of cases, where data are available)
3. Guidelines on Clinical Management of Chikungunya Fever (Ministry of Health, India)