Your code should work fine. You're right about the cause of the nil-operation.
You just have to find the complete node name of your "inputNode".
From python, after your model definition, you can loop over the graph nodes and look for the complete name, in that way:
for n in sess.graph.as_graph_def().node: if "inputNode" in n.name: print(n.name)
Once you got the complete name, you can use it in your Go program.
Also, I suggest you to use a more complete and easy to use wrapper around the tensorflow API: tfgo