timechart - show every week, even if there is no value

Hi, I am creating a timechart and in some of my weeks I have no value for a field ("Number Of Lines"). I need the timechart to present every week, and when there is no value for a week, fill it with value of 0 in the field "Number Of Lines". I have tried fillnull but it is not working. my query: index=testeda_p groupID=sloc_data | eval _time = strptime(dateformat, "%m-%d-%Y") | timechart span=1w sum(sloc) as "Number Of Lines" Thanks