Bug Fix for the Custom Code Node. Nodes will keep the code when reopened.

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Presenters/CustomCodeNodePresenter.cs

             if (codeEditorPopup == null)
             {
                 codeEditorPopup = new CodeEditorPopup(tNode);
-                tNode.Code = "//Write your function below.\r\nvoid test(float a, float b, out float c)\r\n{\r\n\tc = a + b;\r\n}\r\n";
+                if (string.IsNullOrEmpty(tNode.Code))
+                {
+                    tNode.Code = "//Write your function below.\r\nvoid test(float a, float b, out float c)\r\n{\r\n\tc = a + b;\r\n}\r\n";
+                }
             }
 
             string buttonText = codeEditorPopup.IsOpen ? "Close Code Editor" : "Open Code Editor";

MaterialGraphProject/Assets/Code Graph.ShaderGraph.meta

+fileFormatVersion: 2
+guid: 6e7da496d1011f54b8e707ce39eb4b5f
+timeCreated: 1495644036
+licenseType: Pro
+ScriptedImporter:
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
+  script: {fileID: 11500000, guid: 625f186215c104763be7675aa2d941aa, type: 3}