Fieldmapping types with the type none cannot be seperated from actual mapped fields with a $null value. This is very confusing and makes it a bit of a strage mapping type to use. The purpose of a field with mappingtype none would be to return the data from a target using the script, and not set it. It would be way more logical to not provide the fields in the actionContext, because they should not be set. But keep them in the outputContext because they do need to be returned.