Actually, I cannot get the Tutorial code to work, even. This is the code from the section " 2 - Modifying the model to add a different backbone" (which I believe is not used in the rest of the tutorial):
import torch
import torchvision
from torchvision.models.detection import FasterRCNN
from torchvision.models.detection.rpn import AnchorGenerator

backbone = torchvision.models.mobilenet_v2(pretrained=True).features
backbone.out_channels = 1280
anchor_generator = AnchorGenerator(sizes=((32, 64, 128, 256, 512),),
                                   aspect_ratios=((0.5, 1.0, 2.0),))
roi_pooler = torchvision.ops.MultiScaleRoIAlign(featmap_names=[0],
                                                output_size=7,
                                                sampling_ratio=2)
model = FasterRCNN(backbone,
                   num_classes=2,
                   rpn_anchor_generator=anchor_generator,
                   box_roi_pool=roi_pooler)

I try to test it like this:
model.eval()
x = [torch.rand(3, 300, 400), ]
predictions = model(x)


This generates the error message below. What am I doing wrong here? It may be related to a comment that indicates something about features in the general case being dictionaries?
  File ".../tutorial_error.py", line 19, in <module>
    predictions = model(x)
  File "...\venv\lib\site-packages\torch\nn\modules\module.py", line 727, in _call_impl
    result = self.forward(*input, **kwargs)
  File "...\venv\lib\site-packages\torchvision\models\detection\generalized_rcnn.py", line 100, in forward
    detections, detector_losses = self.roi_heads(features, proposals, images.image_sizes, targets)
  File "...\venv\lib\site-packages\torch\nn\modules\module.py", line 727, in _call_impl
    result = self.forward(*input, **kwargs)
  File "...\venv\lib\site-packages\torchvision\models\detection\roi_heads.py", line 752, in forward
    box_features = self.box_roi_pool(features, proposals, image_shapes)
  File "...\venv\lib\site-packages\torch\nn\modules\module.py", line 727, in _call_impl
    result = self.forward(*input, **kwargs)
  File "...\venv\lib\site-packages\torchvision\ops\poolers.py", line 207, in forward
    self.setup_scales(x_filtered, image_shapes)
  File "...\venv\lib\site-packages\torchvision\ops\poolers.py", line 176, in setup_scales
    lvl_min = -torch.log2(torch.tensor(scales[0], dtype=torch.float32)).item()
IndexError: list index out of range