how to create unity custsom terrain shader with shader graph

Question

in unity2019.1, I use lwrp with shader graph, where I use unity terrain, and I want to use a custom shader created by shader graph, but the editor warning "can't use materials with shaders which need tangent gemotery on terrain." But I don't use tangent in shader graph, how could I remove this warning? While I check another shader creator "Amplify Shader Editor", It use a custom function node to use tangent, but I don't konw how to do that in Shader Graph, can anyone help me ?