node.bittrex.api - Error while calling buylimit function

I am conducting some testing and when I call the buylimit function I get an error.

My code is the following:

var assert = require('assert');
var bittrex = require('node.bittrex.api');
var fs = require('fs');
var config = JSON.parse(fs.readFileSync('./config.json'));

bittrex.options({
  'apikey' : config.api.apiBittrex.key,
  'apisecret' : config.api.apiBittrex.secret,
});

bittrex.buylimit({ market : tradingPair, quantity : quantityToBuy, rate : unitPrice }), function( data ) {
  console.log("Order Executed"
}

this generate an order in Bittrex, but the code throw an error pointing to the following code in node.Bittrex.api.js (error in the last "callback" as highlighted below).

var sendRequestCallback = function(callback, op) {
    var start = Date.now();

    request(op, function(error, result, body) {
      ((opts.verbose) ? console.log("requested from " + op.uri + " in: %ds", (Date.now() - start) / 1000) : '');
      if (!body || !result || result.statusCode != 200) {
        var errorObj = {
          success: false,
          message: 'URL request error',
          error: error,
          result: result,
        };
        return ((opts.inverse_callback_arguments) ?
          callback(errorObj, null) :
          callback(null, errorObj));
      } else {
        result = JSON.parse(body);
        if (!result.success) {
          // error returned by bittrex API - forward the result as an error
          return ((opts.inverse_callback_arguments) ?
            callback(result, null) :
            callback(null, result));
        }
        return ((opts.inverse_callback_arguments) ?
          callback(null, ((opts.cleartext) ? body : result)) :
          callback(((opts.cleartext) ? body : result), null));   // -> ERROR HERE
      }
    });
  }

the error says:

Exception has occurred: TypeError TypeError: callback is not a function at Request._callback (c:\00 - Projects\node_modules\node.bittrex.api\node.bittrex.api.js:138:11) at Request.self.callback (c:\00 - Projects\node_modules\request\request.js:186:22) at emitTwo (events.js:126:13) at Request.emit (events.js:214:7) at Request.<anonymous> (c:\00 - Projects\node_modules\request\request.js:1163:10) at emitOne (events.js:116:13) at Request.emit (events.js:211:7) at IncomingMessage.<anonymous> (c:\00 - Projects\node_modules\request\request.js:1085:12) at Object.onceWrapper (events.js:313:30) at emitNone (events.js:111:20)

any help would be much appreciated

dparlevliet / node.bittrex.api

node.bittrex.api - Error while calling buylimit function #102