default Map<String, Object> asMap() {
            final Map<String, Object> map = keys().stream()
                    .map(key -> Pair.with(key, get(key).get()))
                    .collect(Collectors.toMap(Pair::getValue0, Pair::getValue1));
            return Collections.unmodifiableMap(map);
        }
Gets the variables of the {@link Graph} as a {@code Map}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/Graph.java