NodeJS object.keys error

My nodeJS script needs to make a put/post action to provide an xml file as payload.

However it keeps on failing here saying :

     Object.keys(data).forEach(function(key) {
            ^
TypeError: Object.keys called on non-object
    at Function.keys (native)
    at Object.exports.getBodyString

printing data to stdout gives me the whole xml file in text. The type of data is string.

    exports.getBodyString = function(data) {  var body = '';

 if(data && !this.isEmpty(data)){
     Object.keys(data).forEach(function(key) {
      var val = data[key];
      if (exports.isArray(val)) {
       for (var i=0; i<val.length; i++) {
        body += key + '[]=' + encodeURIComponent(val[i]) + '&';
       }
      } else {
       body += key + '=' + encodeURIComponent(val) + '&';
      }
     });
     return body;  }  return null; };

What I try to recreate is:

curl -X POST -H "Content-Type: application/xml" -d @config.xml "http://localhost:11000/oozie/v1/jobs?action=start"

to conclude How do I properly parse a while xml file (indents and new lines and everything) to proper JSON? I'm struggling with xml2js. That seems to return [Object], [Object], ... instead of proper values.