title: How to check if a property has value in Ant
body: <p>I have an Ant XML file which I use for build.</p>
  
  <p>I have 3 properties. I want to break the build if these properties does not contain any value. Also I want to break the build if the value is empty.</p>
  
  <p>How can I do this in Ant?</p>
  
  <p>I a using Ant and not Ant-contrib.</p>