Started a new project, it builds fine and pep8 analysis is correctly printed to the log. Adding the "warnings" module to run as a post-build action, it crashes:

[WARNINGS] Parsing warnings in console log with parser Pep8
ERROR: Publisher hudson.plugins.warnings.WarningsPublisher aborted due to exception
java.lang.NullPointerException
at hudson.plugins.violations.util.AbsoluteFileFinder.addSourcePaths(AbsoluteFileFinder.java:20)
at hudson.plugins.violations.types.pep8.Pep8Parser.parse(Pep8Parser.java:51)
at hudson.plugins.warnings.parser.ViolationsAdapter.parse(ViolationsAdapter.java:60)
at hudson.plugins.warnings.parser.ParserRegistry.parse(ParserRegistry.java:322)
at hudson.plugins.warnings.parser.ParserRegistry.parse(ParserRegistry.java:301)
at hudson.plugins.warnings.WarningsPublisher.parseConsoleLog(WarningsPublisher.java:352)
at hudson.plugins.warnings.WarningsPublisher.perform(WarningsPublisher.java:278)
at hudson.plugins.analysis.core.HealthAwareRecorder.perform(HealthAwareRecorder.java:329)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:710)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:685)
at hudson.model.Build$RunnerImpl.post2(Build.java:162)
at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:632)
at hudson.model.Run.run(Run.java:1463)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:239)
Finished: FAILURE