def GetServiceDll(self, key):
    """Get the Service DLL for a service, if it exists.

    Checks for a ServiceDLL for in the Parameters subkey of a service key in
    the Registry.

    Args:
      key (dfwinreg.WinRegistryKey): a Windows Registry key.

    Returns:
      str: path of the service DLL or None.
    """
    parameters_key = key.GetSubkeyByName('Parameters')
    if not parameters_key:
      return None

    service_dll = parameters_key.GetValueByName('ServiceDll')
    if not service_dll:
      return None

    return service_dll.GetDataAsObject()
Get the Service DLL for a service, if it exists.

    Checks for a ServiceDLL for in the Parameters subkey of a service key in
    the Registry.

    Args:
      key (dfwinreg.WinRegistryKey): a Windows Registry key.

    Returns:
      str: path of the service DLL or None.