Applied patch from jira issue - OFBIZ-904 - Error when "Inventory Facility Id" is left blank in product store settings. 
Thanks Michel for creating the issue and Thanks Arun Arun for providing the patch. 

git-svn-id: https://svn.apache.org/repos/asf/ofbiz/trunk@1639841 13f79535-47bb-0310-9956-ffa450edef68