The AICamera demo that is mentioned as part of the pytorch->onnx->caffe2 tutorial 5 and caffe2 tutorials collected here 3 are out of date and do not match the current API.
I tried looking at the source, but am still getting an error:
  what():  [enforce fail at operator.h:791] . Unsupported type of tensor: nullptr (uninitialized)Error from operator: 
input: "3" input: "0" output: "10" name: "" type: "Gather" device_option { device_type: 0 device_id: 0 }

Here my attempt to do inference
    caffe2::Predictor* pred = new caffe2::Predictor(init_net, predict_net);

    caffe2::CPUContext cpuc;
    std::vector<float> data(5, 0.);
    caffe2::TensorCPU input({1, 5}, data, &cpuc);

    caffe2::Predictor::TensorList input_vec = {input};
    caffe2::Predictor::TensorList output_vec = {}; 

    (*pred)(input_vec, &output_vec);

with a model
class MLP(nn.Module):
    def __init__(self):
        self.fc = nn.Linear(5, 3)

    def forward(self, x):
        return self.fc(x)