As before, setValue("") is equivalent to setNull().
Again, this is the ONLY special feature of strings.

But this time, they both result in the variable being equal to ""
and not null. Both data() and addressOfData will return values
compatible with "", while isNull() will return false.

Note in particular that wrapped attributes and attribute lists are
reinterpreted in such a way that fields are considered equal to ""
both if the corresponding attributes are null and if they are "".


git-svn-id: file:///git/lcgcool.svndb/cool/trunk@8217 4525493e-7705-40b1-a816-d608a930855b