I have two DateTime variables first period and second period and with each period i have a date range between two date for each period. My issue is that i usually set my dates to null withn i load the page but for these dates i cannot set them to null which i would like rather than setting a specific date. 

```
DateTime firstPeriodBeginDate = DateTime.Today.AddMonths(-3);
DateTime secondPeriodBeginDate = DateTime.Today.AddMonths(-2);

```

I would like it set to null so that it will equal to the values selected from the date picker by the user when used to render results.