[BugFix] fix incorrect _bias and bias usage (#4310)

python/dgl/nn/pytorch/conv/gcn2conv.py

@@ -151,7 +151,7 @@ class GCN2Conv(nn.Module):
         nn.init.normal_(self.weight1)
         if not self._project_initial_features:
             nn.init.normal_(self.weight2)
-        if self._bias is not None:
+        if self._bias:
             nn.init.zeros_(self.bias)
 
     def set_allow_zero_in_degree(self, set_value):
@@ -265,8 +265,8 @@ class GCN2Conv(nn.Module):
                     feat_0, feat_0, self.weight2, beta=(1 - self.beta), alpha=self.beta
                 )
 
-            if self._bias is not None:
-                rst = rst + self._bias
+            if self._bias:
+                rst = rst + self.bias
 
             if self._activation is not None:
                 rst = self._activation(rst)

tests/pytorch/test_nn.py

@@ -647,10 +647,11 @@ def test_appnp_conv_e_weight(g, idtype):
 
 @parametrize_idtype
 @pytest.mark.parametrize('g', get_cases(['homo'], exclude=['zero-degree']))
-def test_gcn2conv_e_weight(g, idtype):
+@pytest.mark.parametrize("bias", [True, False])
+def test_gcn2conv_e_weight(g, idtype, bias):
     ctx = F.ctx()
     g = g.astype(idtype).to(ctx)
-    gcn2conv = nn.GCN2Conv(5, layer=2, alpha=0.5,
+    gcn2conv = nn.GCN2Conv(5, layer=2, alpha=0.5, bias=bias,
                            project_initial_features=True)
     feat = F.randn((g.number_of_nodes(), 5))
     eweight = F.ones((g.num_edges(), ))