org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'null' with class 'null' to class 'long'. Try 'java.lang.Long' instead
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.castToNumber(DefaultTypeTransformation.java:163)
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.longUnbox(DefaultTypeTransformation.java:78)
        at nextflow.trace.WorkflowStats.getCpuTime(WorkflowStats.groovy:137)
        at nextflow.trace.WorkflowStats.updateTasksCached(WorkflowStats.groovy:172)
        at nextflow.trace.StatsObserver.onProcessCached(StatsObserver.groovy:80)
        at nextflow.Session.notifyTaskCached(Session.groovy:831)
        at nextflow.Session$notifyTaskCached$1.call(Unknown Source)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
        at nextflow.processor.TaskProcessor.checkCachedOutput(TaskProcessor.groovy:995)
        at nextflow.processor.TaskProcessor$checkCachedOutput$2.callCurrent(Unknown Source)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:52)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:154)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:182)
        at nextflow.processor.TaskProcessor.checkCachedOrLaunchTask(TaskProcessor.groovy:841)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:210)
        at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.callCurrent(PogoMetaMethodSite.java:59)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:52)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:154)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:182)
        at nextflow.processor.TaskProcessor.invokeTask(TaskProcessor.groovy:674)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSite.invoke(PogoMetaMethodSite.java:169)
        at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.call(PogoMetaMethodSite.java:71)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
        at nextflow.processor.TaskProcessor$InvokeTaskAdapter.call(TaskProcessor.groovy:225)
        at groovyx.gpars.dataflow.operator.DataflowOperatorActor.startTask(DataflowOperatorActor.java:120)
        at groovyx.gpars.dataflow.operator.ForkingDataflowOperatorActor.access$001(ForkingDataflowOperatorActor.java:35)
        at groovyx.gpars.dataflow.operator.ForkingDataflowOperatorActor$1.run(ForkingDataflowOperatorActor.java:58)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)