How to manage a value both as a date and as a String?

Within a flow, I collect some data with a Scraping from a Web Page.

Among these:
Due Date, which is clearly a date,
and, Actual Completion, that could be, or date, or string.

That is,
the people who fill in this table, should enter a Date, but often,
leave the field blank, and then the system encodes it as “None”.

In my flow, I need this value, to make a comparison between dates, but if “actual completion” is not a date, I need it to be “None” (string), and nothing else.

Specifically, I have to perform
some operations if “Actual completion” <= Today, or = “None”,
and other operations, if “Actual completion” > Today

How do I manage the cell both as a “data” and as a string?
I have no experience with UiPath and programming, so if you can give me full directions, even those that are basic to you.