properly convert NULL data objects

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1634966 13f79535-47bb-0310-9956-ffa450edef68
PROTON-723: based on gordon's patch, added support for the coordinator target

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1635266 13f79535-47bb-0310-9956-ffa450edef68
removed accidental addition

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1635267 13f79535-47bb-0310-9956-ffa450edef68
bumped the release version on trunk

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1635463 13f79535-47bb-0310-9956-ffa450edef68