Replacing Nulls/30/12/1899 dates in Excel Power Query

Hi Team,

I have been doing power query for data cleaning. I have seen that one of the calendar column (Date/Time) is in "Text" data type. When we try to change the data type in power query as "Date/Time" Data type, all the null rows in that column brings date like 30/12/1899. Can anyone advise on this how to get rid of this dates or replace those dates or nulls to something else we want or may be we can keep as blank?

Thanks!