title: Null string exception
body: <p>Before i ask my question i need to mention that i looked up in the site to solve the problem but i didnt find nothing.</p>
  
  <p>Here is my function : </p>
  
  <pre><code>    public string GetAccessToken(int agencyId)
      {
          string retrunString = null;
          Token fbToken = tokenMgr.Get(agencyId, "FacebookInsights");
          if (String.IsNullOrWhiteSpace(fbToken.AccessToken))  **
              return retrunString;
          else
              return fbToken.AccessToken;
      }
  </code></pre>
  
  <p>When Token is an object which include a String field  name : AccessToken.</p>
  
  <p>When i debug the code and reach the line with the ' ** ' when fbToken.AccessToken is NULL , I get an exception " <strong>Object reference not set to an instance of an object.</strong>"</p>
  
  <p>When i looked up in other threads they suggest to use <strong>String.IsNullOrWhiteSpace</strong> , but it didnt solve the problem and i keep getting the error.</p>
  
  <p>I would greatly appreciate any help , thanks in advance!</p>