zero-mAP fix remove `torch.empty()` forward pass in `.train()` mode (#9068)

utils/loggers/__init__.py

@@ -296,7 +296,7 @@ def log_tensorboard_graph(tb, model, imgsz=(640, 640)):
     try:
         p = next(model.parameters())  # for device, type
         imgsz = (imgsz, imgsz) if isinstance(imgsz, int) else imgsz  # expand
-        im = torch.empty((1, 3, *imgsz)).to(p.device).type_as(p)  # input image
+        im = torch.zeros((1, 3, *imgsz)).to(p.device).type_as(p)  # input image (WARNING: must be zeros, not empty)
         with warnings.catch_warnings():
             warnings.simplefilter('ignore')  # suppress jit trace warning
             tb.add_graph(torch.jit.trace(de_parallel(model), im, strict=False), [])