Get NULL from Excel spreadsheet used for Datasource in SoapUI NG Pro?

We have operational JSON and several fields are set to variables to be populated with the values from an Excel spreadsheet

used as a Datasource.

My question is how do I enter a NULL into the Excel spreadsheet so SoapUI NG Pro inserts that

value into my JSON without quotes?

My JSON has "field": "${DataSource#fieldvalue}",

My desired outcome after the DataSource is read in and populates my JSON is:

"field": NULL,   (not "field": "NULL",)

How to I enter the NULL into the Excel spreadsheet so this works?  I have tried many variations and nothing works.

I also need it do work the same way if I enter numerical values, i.e. "field": 12345,  (not "field":"12345",)