Github user nathanejohnson commented on a diff in the pull request:

    https://github.com/apache/cloudstack/pull/1956#discussion_r102305779
  
    --- Diff: 
engine/orchestration/src/com/cloud/vm/VirtualMachineManagerImpl.java ---
    @@ -744,14 +744,17 @@ protected boolean checkWorkItems(final VMInstanceVO 
vm, final State state) throw
     
         protected <T extends VMInstanceVO> boolean changeState(final T vm, 
final Event event, final Long hostId, final ItWorkVO work, final Step step) 
throws NoTransitionException {
             // FIXME: We should do this better.
    -        final Step previousStep = work.getStep();
    -        _workDao.updateStep(work, step);
    +        Step previousStep = null;
    +        if (work != null) {
    +            previousStep = work.getStep();
    --- End diff --
    
    I'm not sure I'm following.  From reading the code a bit, it looks like the 
only scenario where a false would be returned from stateTransitTo would be 
where the state was not properly persisted to the db.  No exception is thrown 
in that case.  In the current code, false *or* exception will try to revert.  
Also, currently previousStep would *probably* never be null - though if work is 
null this will cause another NPE on line 747 of current code.  In the PR, 
previousStep will *probably* only be null in the case where work is null.
    
    What is the value of making a distinction from a false versus an exception 
in this case?  Me adding a check for previousStep != null is simply to make 
sure that work is not null above.  I could also check work for null here too, 
but I don't think that's what you're getting at.


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