public default void writeVertices(final OutputStream outputStream, final Iterator<Vertex> vertexIterator) throws IOException {
        while (vertexIterator.hasNext()) {
            writeVertex(outputStream, vertexIterator.next());
        }
    }
Write a vertex to a stream without writing its edges.

@param outputStream the stream to write to.
@param vertexIterator a iterator that returns a list of vertices.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/GraphWriter.java