Implement Copy() for GradientShaderProperty

com.unity.shadergraph/Editor/Data/Graphs/GradientShaderProperty.cs

 
         public static Vector4 ColorKeyToVector(GradientColorKey key)
         {
-            return new Vector4( key.color.r, key.color.g, key.color.b, key.time); 
+            return new Vector4( key.color.r, key.color.g, key.color.b, key.time);
-            return new Vector2( key.alpha, key.time); 
+            return new Vector2( key.alpha, key.time);
         }
     }
 
             m_OverrideMembers = true;
             m_OverrideSlotName = slotName;
         }
-        
+
         public override string GetPropertyDeclarationString(string delimiter = ";")
         {
             if(m_OverrideMembers)
         {
             return new GradientNode { gradient = value };
         }
+
+        public override IShaderProperty Copy()
+        {
+            return new GradientShaderProperty
+            {
+                value = value
+            };
+        }
-}
+}