fix 2 bug of eager (#54041)

paddle/fluid/eager/backward.cc

@@ -141,6 +141,7 @@ std::vector<paddle::Tensor> RunBackward(
   std::deque<GradNodeBase*> orig_queue;
   std::unordered_map<GradNodeBase*, std::unique_ptr<GradTensorHolder>>
       node_input_buffers_dict;
+  std::unordered_set<GradNodeBase*> visited;
   for (size_t i = 0; i < tensors.size(); i++) {
     const paddle::Tensor& tensor = tensors[i];
 
@@ -215,6 +216,10 @@ std::vector<paddle::Tensor> RunBackward(
     }
 
     // Prepare queue, potential startup_nodes
+    if (visited.count(grad_node)) {
+      continue;
+    }
+    visited.insert(grad_node);
     queue.push_back(grad_node);
   }
 

paddle/fluid/eager/pylayer/py_layer_node.cc

@@ -163,7 +163,7 @@ GradNodePyLayer::operator()(
                 {paddle::pybind::UnSafeGetTensorFromPyObject(obj)});
           } else if (obj == Py_None) {
             VLOG(4) << "Got None for Tensor with pos: " << i;
-            grad_out.push_back({});
+            grad_out.push_back({paddle::Tensor()});
           } else {
             PADDLE_THROW(phi::errors::InvalidArgument(
                 "We can only support Tensor or None for backward output, "