@Override
    public Object handleExtension(GltfLoader loader, String parentName, JsonElement parent, JsonElement extension, Object input) {
        MaterialAdapter adapter = materialAdapter;
        AssetKey key = loader.getInfo().getKey();
        //check for a custom adapter for spec/gloss pipeline
        if (key instanceof GltfModelKey) {
            GltfModelKey gltfKey = (GltfModelKey) key;
            MaterialAdapter ma = gltfKey.getAdapterForMaterial("unlit");
            if (ma != null) {
                adapter = ma;
            }
        }

        adapter.init(loader.getInfo().getManager());

        return adapter;
    }
Material adapter for the Unlit pipeline
@author Markil 3
jme3-plugins/src/gltf/java/com/jme3/scene/plugins/gltf/UnlitExtensionLoader.java