title: Android Twitter Cannot access callback
body: <p>Im using Twitter 3.0 in my latest app build, and for some reason, I'm getting the error Cannot access callback. "Class file for retrofit2.Callback not found."</p>
  
  <p>I recently upgraded from an older version of the twitter sdk, and this is thje only error I cannot seem to solve. Here is thew method that is throwing the error...</p>
  
  <pre><code>@Override
          public void success(final Result&lt;TwitterSession&gt; twitterSessionResult) {
              twitterName = twitterSessionResult.data.getUserName();
              prefs.edit().putString(TWITTER_NAME_PREF, twitterName).apply();
              mTwitterAuthClient.requestEmail(twitterSessionResult.data, new Callback&lt;String&gt;() {
                  @Override
                  public void success(Result&lt;String&gt; stringResult) {
                      twitterEmail = stringResult.data;
                      prefs.edit().putString(TWITTER_EMAIL_PREF, twitterEmail).apply();
                      mFragment.twitterInfo(twitterName,
                              twitterEmail);
                      finishLogIn(true, null);
                  }
  </code></pre>
  
  <p>That portion "new Callback()" is giving the error. How can I resolve this?</p>