Data_science_project

I need some guidance on the first part of the final Data Science project. In the mysql database data_science_project, the original table date_purchased changed to date_start was had all "null" values as default what reference do I use to use the function date_add to calculate the date_end if there was no start starts stipulated to begin with? Am I to assume that it is "01-01-2022"?  Your help is much appreciated! 
Thanks!