@Override
    public void writeEdge(final OutputStream outputStream, final Edge e) throws IOException {
        mapper.writeValue(outputStream, e);
    }
Writes an {@link Edge} object to the stream.  Note that this format is different from the format of an
{@link Edge} when serialized with a {@link Vertex} as done with
{@link #writeVertex(OutputStream, Vertex, Direction)} or
{@link #writeVertices(OutputStream, Iterator, Direction)} in that the edge label is part of the object and
vertex labels are included with their identifiers.

@param outputStream the stream to write to.
@param e the edge to write.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/graphson/GraphSONWriter.java