title: TypeError: Cannot read property 'unmask' of undefined at Receiver.unmask
body: <p>Launch karma in chrome browser and abru[tly close itself with an Error while running karma for unit testing in angular 2 : </p>
  
  <blockquote>
    <p>19 04 2017 19:14:27.848:ERROR [karma]: TypeError: Cannot read property 'unmask' of undefined<br>
        at Receiver.unmask (C:\Projects\Git Repo\TDP\switchmanager\src\SwitchDesigner\node_modules\engine.io\node_modules\ws\lib\Receiver.js:306:46)<br>
        at Receiver.finish (C:\Projects\Git Repo\TDP\switchmanager\src\SwitchDesigner\node_modules\engine.io\node_modules\ws\lib\Receiver.js:505:25)<br>
        at Receiver.expectHandler (C:\Projects\Git Repo\TDP\switchmanager\src\SwitchDesigner\node_modules\engine.io\node_modules\ws\lib\Receiver.js:493:33)<br>
        at Receiver.add (C:\Projects\Git Repo\TDP\switchmanager\src\SwitchDesigner\node_modules\engine.io\node_modules\ws\lib\Receiver.js:103:24)
        at Socket.realHandler (C:\Projects\Git Repo\TDP\switchmanager\src\SwitchDesigner\node_modules\engine.io\node_modules\ws\lib\WebSocket.js:825:20)<br>
        at emitOne (events.js:96:13)<br>
        at Socket.emit (events.js:188:7)<br>
        at readableAddChunk (_stream_readable.js:176:18)<br>
        at Socket.Readable.push (_stream_readable.js:134:10)<br>
        at TCP.onread (net.js:548:20)<br></p>
  </blockquote>
  
  <p>Any help?</p>