Fix - False positive when content has some empty values.

[KevinJump]

Sometimes you will get false posistive content changes, when the content item has empty values.
this is because the empty value sometimes comes to usync as an empty value and sometimes it isn't included , so the xml can be diffrent.

65d8217 adds an extra bit of XML to markate an empty value node - this means we will get better matches and less false posistives when checking content.