dateTrans Error: Unparseable date: ""

hello,

I've a source field datesource type date and

a target field datetarget type string

datesource = yyyymmdd and i need in datetarget = ddmmyyyy.

i'm using the function dateTtrans, however the follow error occurs:

Runtime exception during processing target field mapping /ns1:file/Inv/InvSum/EDate. The message is: Unparseable date: "" com.sap.aii.mappingtool.tf3.MessageMappingException: Runtime exception during processing target field mapping /ns1:file/Inv/InvSum/EDate. The message is: Unparseable date: ""

thanks very much