diff --git a/src/TensorFlowNET.Core/Operations/ControlFlows/CondContext.cs b/src/TensorFlowNET.Core/Operations/ControlFlows/CondContext.cs
index d525dc66..1bfa81f2 100644
--- a/src/TensorFlowNET.Core/Operations/ControlFlows/CondContext.cs
+++ b/src/TensorFlowNET.Core/Operations/ControlFlows/CondContext.cs
@@ -73,9 +73,9 @@ namespace Tensorflow.Operations
                 // Use the real value if it comes from outer context. This is needed in
                 // particular for nested conds.
                 if (_external_values.ContainsKey(val.name))
-                    result = _external_values[val.name];
-                else
-                    result = val;
+                    result = _external_values[val.name];
+
+                result = result == null ? val : result;
             }
             else
             {
@@ -89,6 +89,11 @@ namespace Tensorflow.Operations
                     _external_values[result.name] = result;
                 }
                 
+                // for debug purpose
+                if(ops.get_default_graph()._nodes_by_name.Count > 60)
+                {
+                }
+
                 with(ops.control_dependencies(null), ctrl =>
                 {
                     var (r0, r1) = control_flow_ops._SwitchRefOrTensor(result, _pred);
diff --git a/src/TensorFlowNET.Core/Operations/Operation.cs b/src/TensorFlowNET.Core/Operations/Operation.cs
index deab05f1..9f4280d9 100644
--- a/src/TensorFlowNET.Core/Operations/Operation.cs
+++ b/src/TensorFlowNET.Core/Operations/Operation.cs
@@ -279,11 +279,13 @@ namespace Tensorflow
         /// <param name="tensor"> the Tensor to be used as the input at the given index.</param>
         public void _update_input(int index, Tensor tensor)
         {
+            _assert_same_graph(tensor);
+
             var input = _tf_input(index);
-            var output = tensor._as_tf_output();
-            _assert_same_graph( tensor);
-            // Reset cached inputs.
-            _inputs=new InputList(new Tensor[]{ tensor }); // is this right? original code: self._inputs_val=None
+            var output = tensor._as_tf_output();
+
+            // Reset cached inputs.
+            _inputs = null;// new InputList(new Tensor[] { tensor }); // is this right? original code: self._inputs_val=None
             // TODO: implement below code dependencies
             //c_api.UpdateEdge(_graph._c_graph, output, input);
         }