REMOVE FIELD VALUE IN BOOK USING DELUGE

REMOVE FIELD VALUE IN BOOK USING DELUGE

I have a custom script that updates a custom field in books based on a set a rules. But with the way rest api works, I cannot see a custom field if it doesn't have any data in it. Therefore my work around was to set a default value and update later. The question is, how can I remove that default value when updating the field in my script?

Example:
if(custom_Field.contains(defaultValue) == true)
{
new_value = Map();
new_value.put("cf_test",value);
            //Puts new value in field, but keeps the default value already in the field
response= zoho.inventory.updateRecord("Items",booksOrgId,item_id,new_value,"booksConnectionName");
            //Insert Here: Removal of default value

                info response;
}