Runner with json data file, converting null value into "null" value

My question:

I have an api endpoint that will accept null values for a json field. When I import test data from a json file, into the runner and run it, it is converting my json field value from null to “null” and failing.

Details (like screenshots):
From sample test json file

From Request of the Post in runner

How I found the problem:
Using the runner

I’ve already tried:
I don’t know what else to try. My json input data file should be sufficient