compare date value from gridview with current and change row color

hi,

i have date time field in sql database which bind with gridview.

i want on gridview rowdata bound data value of gridview  column compare with current date and if gridview date value is less than from current date so make the row backgroup color to red.

note: i have null values in data base as well so in  many row gridview date column will have null values.

please advice