set text field to null or empty

set text field to null or empty

i have a custom text field with length 36 (to store a GUID) ... i used the mass-update feature of the CRM to "clear out" the values from some records ... now they contain a dash ("-") when i load them up in reports or views, but on the view the field shows empty. wtf?

i've tried several different varieties of code to clear this out, with no positive results:

#1 xmlData=<Potentials><row no="1"><fieldlabel value="MyField"><![CDATA[]]></fieldlabel></row></Potentials>

#2 xmlData=<Potentials><row no="1"><fieldlabel value="MyField"></fieldlabel></row></Potentials>

#3 xmlData=<Potentials><row no="1"><fieldlabel value="MyField">NULL</fieldlabel></row></Potentials>

#4 xmlData=<Potentials><row no="1"><fieldlabel value="MyField"><![CDATA[null]]></fieldlabel></row></Potentials>

#5 xmlData=<Potentials><row no="1"><fieldlabel value="MyField">son of a _____</fieldlabel></row></Potentials>

in then end i have two questions:

Q1: has anyone been able to clear out a value programatically? if so, please share.

Q2: why does the UI set the value to a dash on reports/views/export?

cheers,
-e