Project set up with mercurial scm. When trying to do a build, I get the following error.

Started by user kstevens
Building in workspace /usr/local/tomcat/.hudson/jobs/stratinit/workspace
FATAL: null
java.lang.NullPointerException
at hudson.tools.ToolInstaller.preferredLocation(ToolInstaller.java:115)
at hudson.tools.DownloadFromUrlInstaller.performInstallation(DownloadFromUrlInstaller.java:61)
at hudson.tools.InstallerTranslator.getToolHome(InstallerTranslator.java:61)
at hudson.tools.ToolLocationNodeProperty.getToolHome(ToolLocationNodeProperty.java:107)
at hudson.tools.ToolInstallation.translateFor(ToolInstallation.java:150)
at hudson.tasks.Maven$MavenInstallation.forNode(Maven.java:515)
at hudson.maven.MavenModuleSetBuild.getEnvironment(MavenModuleSetBuild.java:173)
at hudson.plugins.mercurial.MercurialSCM.clone(MercurialSCM.java:562)
at hudson.plugins.mercurial.MercurialSCM.checkout(MercurialSCM.java:421)
at hudson.model.AbstractProject.checkout(AbstractProject.java:1195)
at hudson.model.AbstractBuild$AbstractRunner.checkout(AbstractBuild.java:579)
at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:468)
at hudson.model.Run.run(Run.java:1408)
at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:481)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:238)