NullPointerException at GlobalTimerService.getTimerJobInstances in BPM Suite 6

Issue

• When I try to abort a process instance via business-central, it throws NullPointerException and I cannot abort.
• When starting a process with a timer after an exception, it throws NullPointerException and does not start.

Caused by: java.lang.NullPointerException
    at org.jbpm.process.core.timer.impl.GlobalTimerService.getTimerJobInstances(GlobalTimerService.java:149)
    at org.jbpm.process.core.timer.impl.RegisteredTimerServiceDelegate.getTimerJobInstances(RegisteredTimerServiceDelegate.java:107)
    at org.drools.core.marshalling.impl.ProtobufOutputMarshaller.serializeSession(ProtobufOutputMarshaller.java:213)
    at org.drools.core.marshalling.impl.ProtobufOutputMarshaller.writeSession(ProtobufOutputMarshaller.java:119)
    at org.drools.core.marshalling.impl.ProtobufMarshaller.marshall(ProtobufMarshaller.java:166)
    at org.drools.core.marshalling.impl.ProtobufMarshaller.marshall(ProtobufMarshaller.java:148)
    at org.drools.persistence.SessionMarshallingHelper.getSnapshot(SessionMarshallingHelper.java:64)
    at org.drools.persistence.info.SessionInfo.update(SessionInfo.java:85)