(example workflow attached)

When trying to plan a zero node dax:

2012.04.16 08:09:25.947 PDT: [ERROR] **Parsing ** Line: 35
[org.xml.sax.SAXParseException: cvc-complex-type.2.4.b: The content of element 'adag' is not complete. One of '

{"http://pegasus.isi.edu/schema/DAX":executable, "http://pegasus.isi.edu/schema/DAX":transformation, "http://pegasus.isi.edu/schema/DAX":job, "http://pegasus.isi.edu/schema/DAX":dag, "http://pegasus.isi.edu/schema/DAX":dax}

' is expected.]

2012.04.16 08:09:26.177 PDT: [FATAL ERROR]
[1] java.lang.NullPointerException: null at edu.isi.pegasus.planner.refiner.DeployWorkerPackage.addSetupNodesWithoutUntarNodes(DeployWorkerPackage.java:832)
2012.04.16 08:09:26.177 PDT: [WARNING] Non-zero exit-code 1

Zero node daxes are useful in workflows where a previous step determines the size of a subworkflow, where the size of the problem can be [0..n]. I think this is something we should support, so I suggest changing both the schema and the planner.