Resetting a leadSource value on a Customer Record

I am trying to update a Customer record leadSource field to nothing (resetting the value) using NetSuite REST endpoints. Sending anything other then the valid value results in an error: "Error while accessing a resource. Please enter value(s) for: Lead Source.".

Usually when you want to reset fields like parent, category, price level, terms etc. you would do something like this and it would reset the value to nothing.

{"priceLevel": null}

The above does not work for leadSource, Campaigns are enabled on the account. Any suggestions ?

I have tried setting the value to everything under the sun nothing goes through.