Blank values get written out differently from a save compared to an export

[KevinJump]

When you save a content or media item with a null/blank value the XML contains a blank item

<test>
  <value></value>
</text>

however, if you export it (via the dashboard) it gets wrapped in cdata

<test>
  <value><![CDATA[]]></value>
</test>

this is because when you save the content, Umbraco tells you the value is null when we export it, Umbraco says its blank, and we treat these slightly differently.

[KevinJump]

#883b3b1a39b5683be02b9ddcab87334211ba2498 fixes this, by wrapping nulls in cdata sections too.