It looks like in Queue (on or about line 520) the choose method tried to
get the assigned label

...
private JobOffer choose(Task p) {
if (Hudson.getInstance().isQuietingDown())

{ // if we are quieting down, don't run anything so that // all executors will be free. return null; }

Label l = p.getAssignedLabel();
...

And for some reason, in the batch_task the owner is not set, therefore NPE!

...
public Label getAssignedLabel()

{ --> Node on owner.getLastBuiltOn(); if(on==null) return null; return on.getSelfLabel(); }

...

with the following trace.

java.lang.NullPointerException
at hudson.plugins.batch_task.BatchTask.getAssignedLabel(BatchTask.java:93)
at hudson.model.Queue.choose(Queue.java:517)
at hudson.model.Queue.pop(Queue.java:437)
at hudson.model.Executor.run(Executor.java:72)

As there are no tests around this task (shame shame) it is not clear how this is
to work.

I tried to put guards around the calls, but they are all over (shame shame,
inline a method or something)

This is killing slaves in our system.

I am going to try to create a patch, and I may submit it. Not sure where you are
at on this.