@Override
        public Vertex next() {
            try {
                return readVertexInternal(vertexMaker, edgeMaker, d, input);
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }
        }
Supply a mapper {@link GryoMapper} instance to use as the serializer for the {@code KryoWriter}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/gryo/GryoReader.java