Salesforce - NetSuite Connector - Unexpected Mapping Error

Problem:

I am attempting to view the mapping for the flow from Salesforce Opportunity to Sales Order. I am unable to access the mapping tool to map additional fields.  I am getting the following error:

Solution:

In this instance, "Class" & "Department" were hard-coded on the mapping UI, however no value was hardcoded, therefore the connector was sending a "null" value. 

There are two solutions:

1. If these fields are not needed, remove them from the mapping.
2. If you want to retain these fields, set a default value of 'none', instead of leaving it blank.