message: Fix crashing on unknown rank tensors at creating protobuf for converter backend
diff: @@ -492,6 +492,7 @@ def build_toco_convert_protos(input_tensors,
  else:
  shape = input_shapes[idx]
  + if shape.rank is not None:
  # Create shapes with -1 for unknown dimensions.
  dims = []
  for dim in shape:
  