Invalid task configuration causes NPE

I incorrectly used and configured a <service> task instead of a <servicedef> task. When running the build file, ant did not fail with an error message indicating that nested <start>, <verify> or <stop> elements are unsupported. Instead, xharness failed with an NPE:

[testgroup] java.lang.NullPointerException
[testgroup] at org.codehaus.xharness.log.TestLogger.getLogger(TestLogger.java:344)
[testgroup] at org.codehaus.xharness.log.TestLogger.getService(TestLogger.java:262)
[testgroup] at org.codehaus.xharness.log.TestLogger.getService(TestLogger.java:267)
[testgroup] at org.codehaus.xharness.log.TestLogger.taskStartedInternal(TestLogger.java:194)
[testgroup] at org.codehaus.xharness.log.TaskLogger.taskStarted(TaskLogger.java:243)
[testgroup] at org.apache.tools.ant.Project.fireTaskStarted(Project.java:1940)
[testgroup] at org.apache.tools.ant.Task.perform(Task.java:360)
[testgroup] at org.codehaus.xharness.tasks.TestGroupTask.execute(TestGroupTask.java:115)
[testgroup] at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:275)
[testgroup] at org.apache.tools.ant.Task.perform(Task.java:364)
[testgroup] at org.codehaus.xharness.tasks.TestGroupTask.execute(TestGroupTask.java:115)
[testgroup] at org.codehaus.xharness.tasks.XharnessTask.execute(XharnessTask.java:115)
[testgroup] at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:275)
[testgroup] at org.apache.tools.ant.Task.perform(Task.java:364)
[testgroup] at org.apache.tools.ant.Target.execute(Target.java:341)
[testgroup] at org.apache.tools.ant.Target.performTasks(Target.java:369)
[testgroup] at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1216)
[testgroup] at org.apache.tools.ant.Project.executeTarget(Project.java:1185)
[testgroup] at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:40)
[testgroup] at org.apache.tools.ant.Project.executeTargets(Project.java:1068)
[testgroup] at org.apache.tools.ant.Main.runBuild(Main.java:668)
[testgroup] at org.apache.tools.ant.Main.startAnt(Main.java:187)
[testgroup] at org.apache.tools.ant.launch.Launcher.run(Launcher.java:246)
[testgroup] at org.apache.tools.ant.launch.Launcher.main(Launcher.java:67)