The code looks very good, was very hyped to try it but I'm primarily using unity version above 2019.1 and it seems like shader graph classes are now internally implemented is internal and no longer work.
https://forum.unity.com/threads/unable-to-create-custom-shader-graph-node-due-to-inaccessibility-of-customfunctionnode-class.586876/
But there is hope for the upcoming version 7.0.0
https://github.com/Unity-Technologies/ScriptableRenderPipeline/blob/master/com.unity.shadergraph/CHANGELOG.md