NPE during build from parent but not from child

The build is a bit large (~50+) modules for me to post, but the rough layout is like so:

super

As part of the build of super, it fails with the exception below; as part of the build of sub, it succeeds.

[ERROR] Internal error: java.lang.NullPointerException -> [Help 1]
org.apache.maven.InternalErrorException: Internal error: java.lang.NullPointerException
at org.apache.maven.lifecycle.internal.BuilderCommon.handleBuildError(BuilderCommon.java:140)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:98)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:58)
at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:252)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:100)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:443)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:166)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:130)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: java.lang.NullPointerException
at org.apache.maven.plugin.DefaultPluginDescriptorCache$CacheKey.<init>(DefaultPluginDescriptorCache.java:148)
at org.apache.maven.plugin.DefaultPluginDescriptorCache.createKey(DefaultPluginDescriptorCache.java:61)
at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getPluginDescriptor(DefaultMavenPluginManager.java:125)
at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getMojoDescriptor(DefaultMavenPluginManager.java:245)
at org.apache.maven.plugin.DefaultBuildPluginManager.getMojoDescriptor(DefaultBuildPluginManager.java:199)
at org.apache.maven.lifecycle.internal.LifecycleExecutionPlanCalculatorImpl.calculateForkedLifecycle(LifecycleExecutionPlanCalculatorImpl.java:555)
at org.apache.maven.lifecycle.internal.LifecycleExecutionPlanCalculatorImpl.calculateForkedExecutions(LifecycleExecutionPlanCalculatorImpl.java:520)
at org.apache.maven.lifecycle.internal.LifecycleExecutionPlanCalculatorImpl.setupMojoExections(LifecycleExecutionPlanCalculatorImpl.java:160)
at org.apache.maven.lifecycle.internal.LifecycleExecutionPlanCalculatorImpl.calculateExecutionPlan(LifecycleExecutionPlanCalculatorImpl.java:123)
at org.apache.maven.lifecycle.internal.BuilderCommon.resolveBuildPlan(BuilderCommon.java:97)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:82)
... 16 more
[ERROR]
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/InternalErrorException