DimmDeviceType causing issues during node allocation

I can't allocate a node using the DimmDeviceType for the "Memory" section of node composition as I should. In the PODM user guide this field is nullable and I should be able to get this first node composition to work. As you can see the only difference between the first attempt (which fails) and the second (which succeeds) is "DimmDeviceType": null.

root@maas-dev:~# curl -s -k -u admin:admin -XPOST -H "Content-Type: application/json" -d '{"EthernetInterfaces": [{"SpeedMbps": null, "PrimaryVLAN": null}], "Processors": [{"InstructionSet": null, "TotalCores": 2, "AchievableSpeedMHz": null, "Model": null}], "LocalDrives": [{"CapacityGiB": 8.0, "Interface": null, "Type": null, "SerialNumber": null, "MinRPM": null}], "Memory": [{"SpeedMHz": null, "CapacityMiB": 1024, "DataWidthBits": null, "DimmDeviceType": null}]}' https://10.3.0.1:8443/redfish/v1/Nodes/Actions/Allocate
{
  "error" : {
    "code" : "Base.1.0.InvalidPayload",
    "message" : "Request payload is invalid or missing",
    "@Message.ExtendedInfo" : [ ]
  }
}root@maas-dev:~# curl -s -k -u admin:admin -X POST -H "Content-Type: application/json" -d '{"EthernetInterfaces": [{"SpeedMbps": null, "PrimaryVLAN": null}], "Processors": [{"InstructionSet": null, "Totalores": 2, "AchievableSpeedMHz": null, "Model": null}], "LocalDrives": [{"CapacityGiB": 8.0, "Interface": null, "Type": null, "SerialNumber": null, "MinRPM": null}], "Memory": [{"SpeedMHz": null, "CapacityMiB": 1024, "DataWidthBits": null}]}' https://10.3.0.1:8443/redfish/v1/Nodes/Actions/Allocate
root@maas-dev:~#