I worked with the pytorch tutorial for static quantization 5 and when running the line:
torch.quantization.convert(per_channel_quantized_model, inplace=True)

I receive the following warning:
.../torch/quantization/observer.py:845: 
UserWarning: must run observer before calling calculate_qparams. Returning default scale and zero point 

I call the convert function within the following lines of code:
per_channel_quantized_model = load_model(..)
per_channel_quantized_model.eval()
per_channel_quantized_model.fuse_model()
per_channel_quantized_model.qconfig = torch.quantization.get_default_qconfig('fbgemm')
print(per_channel_quantized_model.qconfig)
torch.quantization.prepare(per_channel_quantized_model, inplace=True)
evaluate(per_channel_quantized_model, ...)
torch.quantization.convert(per_channel_quantized_model, inplace=True)

Does somebody have an idea what the warning means and how I can avoid that? I appreciate any hints and suggestions!