fix date emitter on empty strings
fix date emitter on empty strings

https://www.commcarehq.org/hq/pillow_errors/edit_errors/?error=177141

qedsoftware/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq