title: Add values to an existing session without removing values
body: <p>I am looking into adding new values to an existing session. That session will have values in it and I hope that when I add these new ones into it, it would not remove whatever values that is already in that session. E.g. Before adding, the session has 1 value in it. After adding, it should show 2 values in it.
  This is what I have tried:</p>
  <pre><code>     List&lt;string&gt; toAdd = Session[&quot;SendData&quot;] as List&lt;string&gt; ??new List&lt;string&gt;();
       toAdd.Add(TxtData.Text.Trim());
       Session[&quot;behzadList&quot;] = behzadList;
  </code></pre>
  <p>I know that there is already some solutions regarding to this problem( the code above is 1 of them)  However, when I tried this code, whatever values that were already in the session is being removed and the new values that I have just add would appear instead. So I am not too sure is there any other ways to solve this problem.</p>
  <p>Thanks in advance.</p>