Coverage is undefined

I ma trying to generate some coverage for my tests in Protractor. I am using Istanbul Istanbul and also I am following this tutorial: coverage My code inside [protr.conf.js is this:

var istanbul = require('istanbul');
var collector = new istanbul.Collector();
var reporter;
var waitPlugin = require('./src/test/javascript/waitPlugin.js');

function report() {
    if (reporter) {
      reporter.add('html');
      reporter.write(collector, true, function () {
        console.log('Coverage report successfully written');
      });
    }
  }
exports.config = {
    baseUrl: 'http://localhost:8080/#/',

    // use npm run e2e
    specs: [
        './e2e/*.e2e.js'
    ],
    exclude: [],

    framework: 'jasmine2',
   
        //path: 'node_modules/protractor-istanbul-plugin'
        plugins: [{ 
            path: './src/test/javascript/waitPlugin.js'
       
          }
        
        ],

      
    allScriptsTimeout: 110000,

    directConnect: true,

    capabilities: {
        'browserName': 'chrome',
        'chromeOptions': {
            'args': ['show-fps-counter=true']
        }
    },
    onPrepare: function() {
        browser.ignoreSynchronization = false;

        var jasmineEnv = jasmine.getEnv();
        waitPlugin.setOnComplete(report);
        browser.driver.manage().window().maximize();
       // browser.get('${testPortalAddress}');
    
        jasmineEnv.addReporter(new function () {
          this.specDone = function (spec) {
            if (spec.status !== 'failed') {
              var name = spec.fullName.replace(/ /g, '_');
              var reportfile = 'coverage/integration/json/' + name;
              reporter = new istanbul.Reporter(undefined, reportfile);
              var promise = browser.driver.executeScript('return __coverage__;')
                      .then(function (coverageResults) {
                        collector.add(coverageResults);
                      });
              waitPlugin.waitList.push(promise);
            }
          };
        });




    },
    useAllAngular2AppRoots: false
};

I have a waitPlugin.js in my project so this has no problems. But I ma getting this error that I do not know how to fix:

    Fail:  ./src/test/javascript/waitPlugin.js Plugin Tests
[22:39:32] E/plugins -          Failure during teardown: unknown error: __coverage__ is not defined
  (Session info: chrome=70.0.3538.102)

Sorry I am just a beginner.