Can you share code you have on workflow activity

if you are looking at body then it might be issue since there is nothing in res body.

you can do something like (just comment out .getBody() line from your code and use status field to check if it was success or not.)

var r = new sn_ws.RESTMessageV2('AirWatch API', 'delete');

var response = r.execute();
//var responseBody = response.getBody();
var httpStatus = response.getStatusCode();
if (httpStatus == 200) {
    answer = 'yes';
} else {
    answer = 'no';
}