TensorRT: virtual nvinfer1::ILayer* nvinfer1::Network::getLayer(int) const: Assertion `layerIndex >= 0' failed.

After solving the [TensorRT] ERROR: Network must have at least one output

Another error happened

The code is:

# The Onnx path is used for Onnx models.
def build_engine_onnx(model_file):
  print('debug1')
  with trt.Builder(TRT_LOGGER) as builder, builder.create_network() as network, trt.OnnxParser(network, TRT_LOGGER) as parser:
    print('debug2')
    builder.max_workspace_size = common.GiB(1)
    print('debug3')
    # Load the Onnx model and parse it in order to populate the TensorRT network.
    with open(model_file, 'rb') as model:
      print('debug4')
      parser.parse(model.read())
      print('debug5')
    last_layer = network.get_layer(network.num_layers - 1)
    # Check if last layer recognizes it's output
    if not last_layer.get_output(0):
        # If not, then mark the output using TensorRT API
        network.mark_output(last_layer.get_output(0))
    return builder.build_cuda_engine(network)

The output is:

debug1
debug2
debug3
debug4
[libprotobuf WARNING google/protobuf/io/coded_stream.cc:604] Reading dangerously large protocol message.  If the message turns out to be larger than 2147483647 bytes, parsing will be halted for security reasons.  To increase the limit (or to disable these warnings), see CodedInputStream::SetTotalBytesLimit() in google/protobuf/io/coded_stream.h.
[libprotobuf WARNING google/protobuf/io/coded_stream.cc:81] The total number of bytes read was 765571023
debug5
python: ../builder/Network.cpp:863: virtual nvinfer1::ILayer* nvinfer1::Network::getLayer(int) const: Assertion `layerIndex >= 0' failed.
Aborted (core dumped)
(tensorrt) nvidia@Dell:~/Desktop/onnx_trt$ 

My pytorch version is 1.3.0. My tensorrt version is 6.0.1.5.

Which situation lead to this problem? Thanks.