I ran into this issue via org.apache.poi.ss.usermodel.DateUtil.isCellDateFormatted. Essentially, the issue is that I'm working with xlsx spreadsheets that do not contain a <cellStyleXfs/> section. The /cellXfs xf.xfId/ attributes are set to "0". Instead of blowing up, I'd like poi to recognize that there is no such named style and proceed normally.
Created attachment 30921 [details] Patch to avoid ArrayIndexOutOfBoundsExeception.
Thanks for this, patch applied in r1534818.