ONNX and tensorRT

Hi,

I have tried creating a TensorRT engine from an ONNX exported file from pyTorch 1.0 and failed.
II exported a model to ONNX from pytorch 1.0, and tried to load it to tensorRT using:

def build_engine_onnx(model_file):
    with trt.Builder(TRT_LOGGER) as builder, builder.create_network() as network, trt.OnnxParser(network, TRT_LOGGER) as parser:
        builder.max_workspace_size = common.GiB(1)
        # Load the Onnx model and parse it in order to populate the TensorRT network.
        with open(model_file, 'rb') as model:
            parser.parse(model.read())
        return builder.build_cuda_engine(network)
build_engine_onnx(model_path)

I have received the following error:

ERROR: Network must have at least one output.

When I tried to print the model, I get:

output {
    name: "output1"
    type {
      tensor_type {
        elem_type: FLOAT
        shape {
          dim {
            dim_value: 1
          }
          dim {
            dim_value: 17
          }
          dim {
            dim_value: 56
          }
          dim {
            dim_value: 64
          }
        }
      }
    }
  }
}
opset_import {
  version: 9
}

tensorRT supports opset 7. Is there a way to save the model in opset 7? The converter in onnx utilities crash.