fix(networks): support QuickNAT without optional SE blocks

Signed-off-by: kyinhub <kevinpyin@gmail.com>

Author: yinkev

monai/networks/nets/quicknat.py

@@ -43,7 +43,16 @@ class SkipConnectionWithIdx(SkipConnection):
     """
 
     def forward(self, input, indices):  # type: ignore[override]
-        return super().forward(input), indices
+        submodule_output, _ = self.submodule(input, None)
+        if self.mode == "cat":
+            output = torch.cat([input, submodule_output], dim=self.dim)
+        elif self.mode == "add":
+            output = torch.add(input, submodule_output)
+        elif self.mode == "mul":
+            output = torch.mul(input, submodule_output)
+        else:
+            raise NotImplementedError(f"Unsupported mode {self.mode}.")
+        return output, indices
 
 
 class SequentialWithIdx(nn.Sequential):

tests/networks/nets/test_quicknat.py

@@ -36,6 +36,14 @@
 ]
 
 
+class TestQuicknatCore(unittest.TestCase):
+    def test_forward_without_optional_se_dependency(self):
+        net = Quicknat(num_classes=2, num_channels=1, num_filters=4, se_block=None)
+        with eval_mode(net):
+            result = net(torch.randn(1, 1, 32, 32))
+        self.assertEqual(result.shape, (1, 2, 32, 32))
+
+
 @unittest.skipUnless(has_se, "squeeze_and_excitation not installed")
 class TestQuicknat(unittest.TestCase):
     @parameterized.expand(TEST_CASES)