Getting the sessionId of a session running in nightwatch

googleTest.js

module.exports = {
  "Demo test Google" : function (browser) {
    browser.session(function(session) {
      console.log(session.sessionId);
    });
    browser
      .url("http://www.google.com")
      .waitForElementVisible('body', 1000)
      .setValue('input[type=text]', 'nightwatch')
      .waitForElementVisible('button[name=btnG]', 1000)
      .click('button[name=btnG]')
      .pause(1000)
      .assert.containsText('#main', 'The Night Watch')
      .end();
  }
};