Fixes https://issues.apache.org/jira/browse/OFBIZ-5272 "Sales by Store report generates an error"

jleroux: I vaguely remember a change related to ignore-if-null and ignore-if-empty. Anyway replacing ignore-if-null by ignore-if-empty does the trick, which makes sense

git-svn-id: https://svn.apache.org/repos/asf/ofbiz/trunk@1512573 13f79535-47bb-0310-9956-ffa450edef68