private static Onnx.NodeProto getNodeFromGraph(String nodeName, Onnx.GraphProto graph) {
        Optional<Onnx.NodeProto> node = getNodeFromGraphNames(nodeName, graph);
        if (node.isPresent())
            return node.get();

        node = getNodeFromGraphOutputs(nodeName, graph);
        if (node.isPresent())
            return node.get();

        node = getNodeFromGraphInputs(nodeName, graph);
        if (node.isPresent())
            return node.get();

        throw new IllegalArgumentException("Node '" + nodeName + "' not found in ONNX graph");
    }
Converts an ONNX graph to a Vespa IntermediateGraph which is the basis
for generating Vespa ranking expressions.

@author lesters
model-integration/src/main/java/ai/vespa/rankingexpression/importer/onnx/GraphImporter.java