title: Are Java system properties always non-null?
body: <p>There are a couple of <a href="http://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html">Java system properties</a>, among them things like <code>java.home</code> and <code>path.separator</code>, <code>user.home</code>. The <a href="http://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html">spec</a> does not mention any formal promises on the existence of those values. </p>
  
  <p>Especially I am interested in <code>user.home</code>. Does it always point to some existing path?</p>