<code>String</code> (or <code>null</code>) policy context 
 identifier established for the thread. This method must 
 return the default policy context 
 identifier, <code>null</code>, if the policy context
 identifier of the thread has not been set via <code>setContext</code>
 to another value.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="http://docs.oracle.com/javase/8/docs/api/java/lang/SecurityException.html?is-external=true" title="class or interface in java.lang">SecurityE