Description of problem:
I have a simple CIM provider written using pywbem + cmpi-bindings and I
get traceback when it parses xml with NULL values, for example when
processing ModifyInstance:

<CIM CIMVERSION="2.0" DTDVERSION="2.0">
  <MESSAGE ID="1001" PROTOCOLVERSION="1.0">
    <SIMPLEREQ>
      <IMETHODCALL NAME="ModifyInstance">
        <LOCALNAMESPACEPATH>
          <NAMESPACE NAME="root"/>
          <NAMESPACE NAME="cimv2"/>
        </LOCALNAMESPACEPATH>
        <IPARAMVALUE NAME="ModifiedInstance">
...
           <PROPERTY NAME="InstallDate" TYPE="datetime"/>

Results into a traceback in cmpi2pywbem_inst():

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/cmpi_pywbem_bindings.py", line
82, in __call__
    return self.meth(*args, **kwds)
  File "/usr/lib/python2.7/site-packages/cmpi_pywbem_bindings.py", line
492, in set_instance
    pinst = self.cmpi2pywbem_inst(newinst)
  File "/usr/lib/python2.7/site-packages/cmpi_pywbem_bindings.py", line
696, in cmpi2pywbem_inst
    _type, is_array = _cmpi_type2string(data.type)
AttributeError: 'NoneType' object has no attribute 'type'


The reason is that cmpiinst.get_property_at(i) returns data as None,
while cmpi2pywbem_inst expects that data.type exists.


Version-Release number of selected component (if applicable):
cmpi-bindings-pywbem-0.4.17-2