Better initialization in gradient node

MaterialGraphProject/Assets/NewNodes/Editor/Keep/GradientNode.cs

     [Title("Input/Gradient")]
     public class GradientNode : AbstractMaterialNode, IGeneratesBodyCode
     {
-        Gradient m_Gradient;
+        Gradient m_Gradient = new Gradient();
 
         [SerializeField]
         Vector4[] m_SerializableColorKeys = { new Vector4(1f, 1f, 1f, 0f), new Vector4(0f, 0f, 0f, 1f), };
             AddSlot(new Vector1MaterialSlot(BOutputSlotId, k_BOutputSlotName, k_BOutputSlotName, SlotType.Output, 0));
             AddSlot(new Vector1MaterialSlot(AOutputSlotId, k_AOutputSlotName, k_AOutputSlotName, SlotType.Output, 0));
             RemoveSlotsNameNotMatching(new[] { TimeInputSlotId, RGBAOutputSlotId, ROutputSlotId, GOutputSlotId, BOutputSlotId, AOutputSlotId });
+
+        }
+
+        public override void OnAfterDeserialize()
+        {
+            base.OnAfterDeserialize();
+            m_SerializableAlphaKeys = null;
+            m_SerializableColorKeys = null;
             m_Gradient.SetKeys(colorKeys, alphaKeys);
         }