title: C# checking for undefined variable received via querystring from JQuery/Ajax call
body: <p>There are many questions discussing this topic with ref to Javascript; but I  could not get any with ref to C#.</p>
  
  <p>Both the 'String........' statements below return <code>false</code>.</p>
  
  <pre><code>     // foll querystring value from JQuery/Ajax call
       var  thisfieldvalue = Request.QueryString["fieldvalue"];
  
       bool boola = String.IsNullOrWhiteSpace(thisfieldvalue );
       bool boolb = String.IsNullOrEmpty(thisfieldvalue );
  </code></pre>
  
  <p>What is the best way to check for Undefined string variable in C#?</p>
  
  <p>Note:<br>
  I get 'Undefined variable' values occasionally, via  the JQuery/Ajax calls with the 'querystring'; and it ends up in the C# variable when I use the statement </p>
  
  <p>var  thisfieldvalue = Request.QueryString["fieldvalue"];</p>
  
  <p>and the 'thisfieldvalue' variable passes both the 'String.IsNullOrWhiteSpace' as well as the 'String.IsNullOrEmpty' checks....</p>
  
  <p>Note 2: I have edited the question again to make my question clearer... I am sorry that earlier it was not that clear.... </p>