How do I set a date field as blank via RESTlet interface?

Our company has integrated with Netsuite using the RESTlet interface. Everything is working fine except for one thing: when we go to create or save a SalesOrder in Netsuite, all of the date fields default to today if we pass in a blank date value.

Here's an example: When we save a SalesOrder and add Items, the Item-level records have the fields RevRecStartDate and RevRecEndDate. On our end, the values we are mapping to those fields in NS are subscription term start and end dates. Some products in our system are open-ended and, therefore, do not have term start/end dates set -- they are left blank. When we sync this data to NS via the RESTlet interface, those blank term start/end dates are mapped to RevRecStartDate and RevRecEndDate. But, when we look at the SO created in NS afterwards, those fields default to today.