set ir based on opset

Author: guschmue

tf2onnx/graph.py

@@ -1040,7 +1040,10 @@ def make_model(self, graph_doc, optimize=False, graph_name="tf2onnx", **kwargs):
         model_proto = helper.make_model(graph, **kwargs)
 
         # set the IR version based on opset
-        model_proto.ir_version = constants.OPSET_TO_IR_VERSION.get(self.opset, model_proto.ir_version)
+        try:
+            model_proto.ir_version = constants.OPSET_TO_IR_VERSION.get(self.opset, model_proto.ir_version)
+        except:
+            logger.error("ir_version override failed - install the latest onnx version")
 
         # optimize the model proto.
         # TODO: this is disabled by default because of bugs in fuse_consecutive_transposes