Leave date field empty (database sandbox)

I have imported a cvs file (table from mysql database) and one of the fields is an date/time field. The problem is that in the wix collection some records for that specific date/time field are empty and so Wix gives me the message to “Change it into a date/time field” for the records where there is no date.
The problem is that I don’t have a date yet. I only complete the date when the article goes out of stock (which is not the case at this moment). So how do I solve that problem because when I click to change it into a date/time field, I get a datepicker. No other possibilities are given and I really need to keep that field empty.

Ok. Just found it… First you need to select a date with the datepicker and afterwards you right click and delete the field in het record… pfff stupid way of working …