SLING-4058 - avoid NPE

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1633572 13f79535-47bb-0310-9956-ffa450edef68
SLING-4058 - more logging

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1633574 13f79535-47bb-0310-9956-ffa450edef68