NPE during packaging.

The following NPE happens when I run maven from the parent in a multi-module project; though it does not occur when I run mvn clean install from within the module itself.

[INFO] [war:war]
[INFO] Packaging webapp
[INFO] Assembling webapp[safe-online-startup-runtime] in [/Users/mbillemo/Documents/workspace/safe-online/safe-online-startup-runtime/target/safe-online-startup-
runtime-1.1-SNAPSHOT]
[INFO] ------------------------------------------------------------------------
[ERROR] FATAL ERROR
[INFO] ------------------------------------------------------------------------
[INFO] null
[INFO] ------------------------------------------------------------------------
[INFO] Trace
java.lang.NullPointerException
at org.apache.maven.plugin.war.util.WebappStructure.getDependencies(WebappStructure.java:109)
at org.apache.maven.plugin.war.util.WebappStructure.analyseDependencies(WebappStructure.java:288)
at org.apache.maven.plugin.war.packaging.DependenciesAnalysisPackagingTask.performPackaging(DependenciesAnalysisPackagingTask.java:46)
at org.apache.maven.plugin.war.AbstractWarMojo.buildWebapp(AbstractWarMojo.java:439)
at org.apache.maven.plugin.war.AbstractWarMojo.buildExplodedWebapp(AbstractWarMojo.java:375) at org.apache.maven.plugin.war.WarMojo.performPackaging(WarMojo.java:181) at org.apache.maven.plugin.war.WarMojo.execute(WarMojo.java:143) at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:451) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:558)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalWithLifecycle(DefaultLifecycleExecutor.java:499)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:478)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:330)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:291)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:142)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:336) at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:129) at org.apache.maven.cli.MavenCli.main(MavenCli.java:287) 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:585)
at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
at org.codehaus.classworlds.Launcher.main(Launcher.java:375)