How to handle Dates in a dataset that are given as "None"?

Hi,
Can you please take a look at this? Click here

The Year Column was string and had couple of “None” Values. So I replaced None with 0000 and then tried to convert the whole column to a date format. But it’s not working. It is saying that Year 0000 is out of range which I know why. How do I handle Nan values in Year Format??