Some .jtr files do not contains the "elapsed" property, and com.sun.javatest.regtest.XMLWriter crashes with a NPE while handling such files:
java.lang.NullPointerException
    at com.sun.javatest.regtest.XMLWriter.getElapsedTime(XMLWriter.java:99)
    at com.sun.javatest.regtest.XMLWriter.<init>(XMLWriter.java:94)
    at com.sun.javatest.regtest.XMLWriter.translateList(XMLWriter.java:308)
    at com.sun.javatest.regtest.XMLWriter.main(XMLWriter.java:336)

I'm attaching a sketch of a trivial patch that uses "totalTime" property when "elapsed" is not available, and falls back to '0' if neither is available.

Reproduced with:
$ ./jtreg -version
jtreg, version 4.1 fcs b05
Installed in /usr/local/home/lahvac/src/jdk/jtreg/lib/jtreg.jar
Running on platform version 1.7.0_11 from /usr/local/home/lahvac/netbeans/jdks/jdk1.7.0_11/jre.
Built with Java(TM) 2 SDK, Version 1.5.0-b64 on November 29, 2012.
Copyright (c) 1999, 2012, Oracle and/or its affiliates. All rights reserved.
Use is subject to license terms.
JCov 2.0-b10 beta
TestNG: version 6.7-201209281340