public static void assertNotNull(Object o, String errorMessage) {
        if (o == null) {
            throw new AssetLoadException(errorMessage);
        }
    }
Parse a json input stream and returns a {@link JsonObject}
@param stream the stream to parse
@return the JsonObject
jme3-plugins/src/gltf/java/com/jme3/scene/plugins/gltf/GltfUtils.java