title: Unsetting Property in Ant and Removing Property in Ant using a condition
body: <p>How do you unset a property in ant? so that is is completely removed as a property?</p>
  
  <pre><code>&lt;condition property="proguard.config" value="proguard.cfg"&gt;
        &lt;isset property="proguarded"/&gt;
  &lt;/condition&gt;
  
  
   &lt;condition property="proguard.config" value=""&gt;
        &lt;not&gt;
        &lt;isset property="proguarded"/&gt;
        &lt;/not&gt;
  &lt;/condition&gt;
  </code></pre>
  
  <p>This would seem to work. However proguard runs even if there is such a property as proguard.config in existence.  So how do I remove proguard.config as a property altogether conditionally?  I know that if proguard sees that there is a proguard.config property at all in the .properties file it is going to run.</p>