Events page - range switching

[euanwm]

Describe the bug
When toggling between various ranges, if you selected a range twice in a row then it would pass a blank / null value. As a workaround, I added in a few lines to catch a null value and instead pass the default range value instead.

To Reproduce
Steps to reproduce the behavior:

1. Go to the events result page
2. Select 30 days from the dropdown
3. Select 30 days again

Expected behavior
Selected ranges - regardless of the amount of times it is selected - shouldn't result in a null value existing.