How to send null to Mapper Target

OIC Version: 21.4.3

Hi Integration Community

I have a simple requirement in OIC where a REST web service returning JSON returns an attribute which is a string but may be null i.e.

{
 "TaxCode": "STANDARD"
}

Or

{
 "TaxCode": null
}

We need to map this to a target REST web service expecting a JSON payload where the value can also be a string or null.

We wire up the source and target attributes using the Mapper and whilst this works fine when the value is populated, if it is null, OIC is sending an empty double-quoted string "". 

{
  "TaxClassification": ""
}

The target web service is then failing because this is not a valid value. We have verified this with the receiving web service provider.