Issue with calling OPCUA method that returns None

[wizoneyena]

Hey there!

I'm rather new to the whole OPCUA thing and dont really know if I am the one messing things up or misunderstood the documentation.

I am trying to call an OPCUA method that takes no input arguments and returns 3 Output arguments:

• ByteString
• ByteString
• UInt32
  One of these ByteString arguments returns None (as intended) from the OPCUA server and that is causing issues in my code.

Here is the simple implementation for calling the method:

async def main():
        async with Client(url=opcua_server_url) as client:
        while True:
            await client.load_data_type_definitions()
            parent = client.get_node(parent_node_id)
            await parent.get_child(method_browse_name)
            result = await parent.call_method(method_browse_name)
            print(result)
            break
asyncio.run(main())

This one runs into the following exceptions: asyncua.ua.uaerrors._base.UaError: Non array Variant of type VariantType.ByteString cannot have value None

I've done some digging and figured I would try editing the uatypes.py file where the exception originates from.
Adding VariantType.ByteString to line 954 in the 'if' statement completely fixes this issue and I receive my result without an issue.
Since this if statement checks if my return value is None and not an array, it then checks if the VariantType is in said list, but for some reason ByteString is not one of them by default.

if self.Value is None and not self.is_array:
            # only some types of Variants can be NULL when not in an array
            if self.VariantType == VariantType.NodeId:
                # why do we rewrite this case and not the others?
                object.__setattr__(self, "Value", NodeId(0, 0))
            elif self.VariantType not in (
                    VariantType.Null,
                    VariantType.String,
                    VariantType.DateTime,
                    VariantType.ExtensionObject,
                    VariantType.UInt32
                    #VariantType.ByteString
            ):
                raise UaError(
                    f"Non array Variant of type {self.VariantType} cannot have value None"
                )

Any ideas how I can fix it / call the method with a different approach so I dont have to edit the lib itself?