Using Search Commands in Data Objects

Is there a way to use search commands like FillNull and/or Eval to clean up the data in a Data Object?

I have these commands working when i run searches but can not figure out how to applie them to my data object

1) I'm trying to add a column for openrates to a pivot - sourcetype="NMG _ Logfile" | stats count AS totalsent, count(eval(viewed>0)) AS "totalopens" | eval openrate = round(totalopens/totalsent,

2) I'm trying to fillin empty values in my data object | fillnull value=NULL

Thanks, John