I'm using the code below in order to add a NIC configured with `DistributedVirtualSwitch` to an existing VM (via [pyVmomi][1]):

    def __AddNIC(si, vmconf_dict, network_name):
        vm = __get_vm(si, vmconf_dict)
        print " Network label : " + network_name

        devices = []
        nicspec = vim.vm.device.VirtualDeviceSpec()
        nicspec.operation = vim.vm.device.VirtualDeviceSpec.Operation.add
        nicspec.device = vim.vm.device.VirtualVmxnet3()
        nicspec.device.wakeOnLanEnabled = True
        nicspec.device.deviceInfo = vim.Description()
        nicspec.device.connectable = vim.vm.device.VirtualDevice.ConnectInfo()
        nicspec.device.connectable.startConnected = True
        nicspec.device.connectable.allowGuestControl = True

        network_objref = _get_mor_by_property(si, vim.dvs.DistributedVirtualPortgroup, network_name)
        dswitch_port_connection = vim.dvs.PortConnection(
            portgroupKey=network_objref.key,
            switchUuid=network_objref.config.distributedVirtualSwitch.uuid
        )
        nicspec.device.backing = vim.vm.device.VirtualEthernetCard.DistributedVirtualPortBackingInfo()
        nicspec.device.backing.port = dswitch_port_connection

        devices.append(nicspec)
        vmconf = vim.vm.ConfigSpec(deviceChange=devices)
        task = vm.ReconfigVM_Task(vmconf)
        tasks.wait_for_tasks(si, [task])


I'm getting the following exception:

>    switchUuid=network_objref.config.distributedVirtualSwitch.uuid
    AttributeError: 'NoneType' object has no attribute 'uuid'


After examination of Vcenter Managed Objects(via [mob][1]) it appears that
**some of the *:`DistributedVirtualPortgroup`* object references does have this (*`VmwareDistributedVirtualSwitch`*) property, while others have this property *`Unset`*.**

I've tried multiple ways to work around that, such as:


 - Setting:
 `switchUuid=None` which yielded:
>`TypeError: Required field "switchUuid" not provided (not @optional)`

 - Setting:
 `dswitch_port_connection = None` which yielded:
>`TypeError: Required field "port" not provided (not @optional)`


**Note:** When I'm using VMware WebClient to configure the above it works perfectly.


So my question is - how can I make adding a NIC like this work?


  [1]: https://github.com/vmware/pyvmomi