default to an empty string user-agent so no exception if blank.
default to an empty string user-agent so no exception if blank.

total-impact/total-impact-webapp,total-impact/total-impact-webapp,Impactstory/total-impact-webapp,total-impact/total-impact-webapp,Impactstory/total-impact-webapp,Impactstory/total-impact-webapp,Impactstory/total-impact-webapp,total-impact/total-impact-webapp