What should go in as an argument to selectSet : Attribute xsi:nil not allowed on element selectSet

Below is from the sample code:

PropertyFilterSpec spec = new PropertyFilterSpec();

      spec.getObjectSet().add(new ObjectSpec());

      spec.getObjectSet().get(0).setObj(objmor);

      spec.getPropSet().addAll(Arrays.asList(new PropertySpec[]{new PropertySpec()}));

      spec.getPropSet().get(0).getPathSet().addAll(Arrays.asList(filterProps));

      spec.getPropSet().get(0).setType(objmor.getType());

      spec.getObjectSet().get(0).getSelectSet().add(null);

      spec.getObjectSet().get(0).setSkip(Boolean.FALSE);

ManagedObjectReference filterSpecRef = vimPort.createFilter(propCollectorRef, spec, true); // This line throws the error below

SOAP Fault -

InvalidRequestFault

Message:

Attribute xsi:nil not allowed on element selectSet, which is not nillable.

while parsing property "skip" of static type boolean

while parsing serialized DataObject of type vmodl.query.PropertyCollector.ObjectSpec

at line 1, column 283

while parsing property "objectSet" of static type ArrayOfObjectSpec

while parsing serialized DataObject of type vmodl.query.PropertyCollector.FilterSpec

at line 1, column 183

while parsing call information for method CreateFilter

at line 1, column 94

while parsing SOAP body

at line 1, column 86

while parsing SOAP envelope

at line 1, column 22

while parsing HTTP request for method createFilter

on object of type vmodl.query.PropertyCollector

at line 1, column 0