title: Create single node if select single node is null
body: <p>I have a program that updates a config file.  For example, the config file may contain:</p>
  
  <pre><code>&lt;configuration&gt;
    &lt;userSettings&gt;
      &lt;setting name="phoneNumber" serializeAs="String"&gt;
        &lt;value&gt;123-456-7890&lt;/value&gt;
      &lt;/setting&gt;
    &lt;/userSettings&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p>To update this config file, I use the following:</p>
  
  <pre><code>XmlNode phoneNumberNode = theConfig.SelectSingleNode("configuration/userSettings/setting[@name='phoneNumber']");
  phoneNumberNode.FirstChild.InnerText = this._cloudPublisherWebURL;
  </code></pre>
  
  <p>Now, during the update I want to update phoneNumber and address.  Address <em>may or may not be</em> in the config file.</p>
  
  <p>If SelectSingleNode is null, I would like to create a node with the given path and set its value.</p>
  
  <pre><code>XmlNode addressNode = theConfig.SelectSingleNode("configuration/userSettings/setting[@name='address']");
  if(addressNode == null)
  {
    //..Create the node here
  }
  </code></pre>
  
  <p>How can I create the node with value at the given path?</p>