title: Empty wix 3.8 property value, without build warnings
body: <p>I have a wix 3.8 msi installer. How can I get rid of this warning?</p>
  
  <pre><code>&lt;Property Id="DB_USER" /&gt;
  ...
  &lt;Control Id="UserEdit" Type="Edit" X="45" Y="45" Width="200" Height="20" Property="DB_USER" Text="{80}" /&gt;
  </code></pre>
  
  <p>"UserEdit" control is initialized as empty, but i get the following build warning:</p>
  
  <pre><code>Property 'DB_USER' does not contain a Value attribute and is not marked as Admin, Secure, or Hidden. The Property element is being ignored.
  </code></pre>
  
  <p>Attempt 1:</p>
  
  <pre><code>&lt;Property Id="DB_USER" Value=""/&gt;
  </code></pre>
  
  <p>gives the following error:</p>
  
  <pre><code>The Property/@Value attribute's value cannot be an empty string. If a value is not required, simply remove the entire attribute.
  </code></pre>
  
  <p>Attempt 2:</p>
  
  <pre><code>&lt;Property Id="DB_USER" Value="[THIS_PROPERTY_DOES_NOT_EXIST]"/&gt;
  </code></pre>
  
  <p>the control is initialized with string "[THIS_PROPERTY_DOES_NOT_EXIST]" instead of getting the value of a property that does not exist.</p>
  
  <p>Attempt 3: with CustomAction that clears content of DB_USER property, having initial value as "-". CustomAction is described within InstallExecuteSequence being After="CostFinalize". Property remains as "-"</p>