Error establishing OPCUA server when passing node with missing opc_path

When passing a node without opc_path (e.g. opc_id="ns=2;s=thermal_power") to OpcUaServer.create_nodes(), creation of the node raises an Exception. Expected behaviour could be either a clear error message stating that at least a leading dot is missing in the opc_id or a check and direct fix of the issue by adding the leading dot. Result: opc_id="ns=2;s=.thermal_power" --> This should work.