how to search documents with null values from C#

rn001

Hi to everybody,

we have three documents where custom20 have the following values:

doc1 - NULL
doc2 - 10
doc3 - 20

We need to know how to create an IManProfileSearchParameters object to find the doc1 in the search result. which value should we set the imProfileCustom20 attribute?

IManProfileSearchParameters filter = DMS.CreateProfileSearchParameters();
filter.Add(imProfileAttributeID.imProfileCustom20, ???);

the following commands return doc2 y doc3 in the search result:
filter.Add(imProfileAttributeID.imProfileCustom20, ">1");
filter.Add(imProfileAttributeID.imProfileCustom20, "<30");

however, we don't know how to get the doc1 where its custom20 = NULL... We have try the empty string, "<1", "NOT 10", etc.

thanks a lot in advance!

Rafael Nieto
Tikit Spain