Deploying an EAR file containing Skinny-WARs (multiple WARs with shared libs in the EAR) to JBoss (AS7), leads sometimes to a NullPointerException.
The problem is, that the class org.camunda.bpm.container.impl.jboss.deployment.processor.ModuleDependencyProcessor.java adds system dependencies to OTHER sibling subdeployment-units. JBoss starts the subdeployment for each WAR file inside the EAR as subdeployment in parallel. This causes concurrency problems, because each WAR subdeployment adds the camunda libs as system dependencies to all other WARs.
The access to ModuleSpecification.addSystemDependency(), which adds the camunda libraries, is not synchronized and finally leads to an inconsistent system-dependency-list containing null values. As a result JBoss throws some times later a NPE:

08:07:58,214 ERROR [MSC service thread 1-47] org.jboss.msc.service.ServiceControllerImpl$StartTask.startFailed:1987 - MSC000001: Failed to start service jboss.deployment.subunit."GUIWF.ear"."CCP_ConfCalc.jar".CONFIGURE_MODULE: org.jboss.msc.service.StartException in service jboss.deployment.subunit."GUIWF.ear"."CCP_ConfCalc.jar".CONFIGURE_MODULE: JBAS018733: Verarbeitung von Phase CONFIGURE_MODULE von subdeployment "CCP_ConfCalc.jar" of deployment "GUIWF.ear" fehlgeschlagen
at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:166)
at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1980)
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1913)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at org.jboss.as.server.deployment.module.ModuleSpecProcessor.createDependencies(ModuleSpecProcessor.java:237)
at org.jboss.as.server.deployment.module.ModuleSpecProcessor.createModuleService(ModuleSpecProcessor.java:182)
at org.jboss.as.server.deployment.module.ModuleSpecProcessor.deployModuleSpec(ModuleSpecProcessor.java:116)
at org.jboss.as.server.deployment.module.ModuleSpecProcessor.deploy(ModuleSpecProcessor.java:79)
at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:159)
... 5 more

The same problem was reported and fixed for the JBoss JSFDependencyProcessor: https://issues.jboss.org/browse/WFLY-2496

We are currently working with camunda release 7.3, but as I looked in the sources, it should still be open.

Solution?
In general, it seems not to be expected, that one Subdeployment unit adds system dependencies to another Subdeployment unit. So I can not present a clean solution, but adding a "synchronized" to the method ModuleDependencyProcessor.addSystemDependency() should decrease the concurrency possibility.