Rest Receiver Adapter fault message

I am testing the Rest receiver post scenario. I am having no issues with successful processing. Whenever there are failures, we get non-200 HTTP errors. I am able to use custom error handling to route the http_result (json format). The problem is the http_result is in JSON format and I was hoping to have the error also in XML format, so that I can write to the file.

Based on the OSS note 2223623, I could use the

'useResponseErrorMessage'

which allows the REST adapter to create XI Application Error message with payload from the original response:

when I use the above parameter and don't use custom error handling, I get the

Could not queue send for message a937bb08-7d4d-11e7-cda2-000000892cfe(OUTBOUND). Reason: java.lang.NullPointerException:::::

I checked the xpi inspector and I saw couple of messages saying 'Cannot generate header map' and 'Sap category = null' . but no more details.

When there is application fault, I get this error. Is there any way to resolve this issue.