title: sysproperty set to value "${value}" when no property is passed to target
body: <p>I am executing a target with paramters as <code>Dcolor=red</code>.I am using this property value to set system property as</p>
  
  <pre><code>&lt;sysproperty key="COLOR" value="${color}" /&gt;
  </code></pre>
  
  <p>If not passing any parameter named <code>-Dcolor</code>, when fetching key <code>COLOR</code> as <code>System.getProperty("COLOR")</code> is returning <code>${color}</code>.</p>
  
  <p>Is this correct behavior. How to handle such scenario ie. setting COLOR as null if no parameter names color is passed.</p>
  
  <p>Please let me know if I am missing basics here. Resource link will be helpfull</p>