Sum(If(Len(field) = 0, 1) or Sum(If(IsNull(field), 1, 0)
or use NullAsValue field; in your load script.
But you cannot count missing values. The former are actual values that evaluate to null, the latter simply do not exist and there is no direct way to count them - they are just empty holes in your table.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein
Thanks for the information, however, my data source here is really null or blank data. Then I uncheck the Suppress Zero-Values and Put "NULL" on the Null Symbol and Missing Symbol on Presentation Tab. Can I consider that as value already for me to count? Or do I still need to do an update script for each blank items with any text?