def to_date(value)
        if value.nil? or value.strip.empty?
          nil
        else
          Date.strptime(value, date_format)
        end
      end
def to_date(value)
        if value.nil? or value.strip.empty?
          nil
        else
          Date.strptime(value, date_format)
        end
      end
Casts a string to a date