Seeing this with the latest 1.5 version of the plugin. Looks similar to JENKINS-12494

Saving reports...
Processing '/x/eng/rtpbld00/scratch/smo/.jenkins/jobs/ocf_qa_merge_result/builds/2013-11-20_12-16-22/testng/testng-results.xml'
java.lang.NullPointerException
at hudson.plugins.testng.results.MethodResultException.trySettingData(MethodResultException.java:47)
at hudson.plugins.testng.results.MethodResultException.<init>(MethodResultException.java:19)
at hudson.plugins.testng.parser.ResultsParser.finishException(ResultsParser.java:351)
at hudson.plugins.testng.parser.ResultsParser.parse(ResultsParser.java:229)
at hudson.plugins.testng.TestNGTestResultBuildAction.loadResults(TestNGTestResultBuildAction.java:97)
at hudson.plugins.testng.Publisher.perform(Publisher.java:109)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:785)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:757)
at hudson.model.Build$BuildExecution.post2(Build.java:183)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:706)
at hudson.model.Run.execute(Run.java:1704)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:230)

This testng file is a merge of 3 separate ones (the tree suite nodes in this one) each of which worked on its own. I'm not certain this is 100% proper expectation, but it seemed to work with an older version of the merging that we did.