ERROR when reducing (onnx) model inputs using Polygraphy

[I] Finished 10 iteration(s) | Passed: 1/10 | Pass Rate: 10.0%
[I] Finished reducing model outputs
[I] Marking model outputs: [Variable (/model.0/stem2a/conv/Conv_output_0): (shape=[1, 16, 320, 320], dtype=float32)]
[I] Reducing model inputs
[I]     RUNNING | Iteration 1 | Approximately 2 iteration(s) remaining
[I]         Marking model inputs: [Variable (/model.0/stem1/act/Relu_output_0): (shape=[1, 32, 320, 320], dtype=float32), Variable (): (shape=None, dtype=None)]
[I]         Running inference with ONNX-Runtime to determine metadata for intermediate tensors.
            This will cause intermediate models to have static shapes.
[!]             The following outputs were not found in the model: {''}.

Start by reproducing the reported Polygraphy model-input reduction with the provided log and inspect how the reduction step handles the unnamed output shown in the error. Trace the ONNX reduction and inference path until the missing output is identified; done means the reduction completes without reporting an output that is not in the model.