javascript - エラー Uncaught TypeError: プロパティ 'onclick' を null に設定できません

Question

Facebook Javascript で「Uncaught TypeError: Cannot set property 'onclick' of null」の 187 行目と 187 行目は次のとおりです。

" button.onclick = function() {"

すべてのコードは次のとおりです。

<script type="text/javascript">
window.fbAsyncInit = function() {
  FB.init({ appId: <?php echo json_encode($this->getApiKey()) ?>, 
        status: true, 
        cookie: true,
        xfbml: true,
        oauth: true});
 FB.Canvas.setSize({ width: 640, height:1500 });
 //FB.Canvas.setAutoResize();
 function updateButton(response) {
    var button = document.getElementById('fb-auth');

    if (response.authResponse == 'null') {
      //user is already logged in and connected
      var userInfo = document.getElementById('user-info');
     FB.api('/me', function(response) {


      });

      button.onclick = function() {
        FB.logout(function(response) {
          var userInfo = document.getElementById('user-info');
          userInfo.innerHTML="";
    });
      };
    } else {
      //user is not connected to your app or logged out
      //button.innerHTML = 'Login';
      button.onclick = function() {
        FB.login(function(response) {
if(response.status=='connected') setLocation('<?php echo $this->getConnectUrl() ?>');
      if (response.authResponse) {
            FB.api('/me', function(response) {
          var userInfo = document.getElementById('user-info');


        });  

          } else {
            //user cancelled login or did not grant authorization
          }
         }, {scope:'email, user_birthday'});    
      }
    }
  }

  // run once with current status and whenever the status changes
  FB.getLoginStatus(updateButton);
  //FB.Event.subscribe('auth.statusChange', updateButton);  
};

(function() {
  var e = document.createElement('script'); e.async = true;
  e.src = document.location.protocol 
    + '//connect.facebook.net/en_US/all.js';
  document.getElementById('fb-root').appendChild(e);
}());

</script>

さらに情報が必要な場合は、助けてくれてありがとうと言ってください。ありがとう！。