private List<String> getStepsAsList(final Traversal.Admin<?,?> t) {
            final List<String> steps = new ArrayList<>();
            t.getSteps().iterator().forEachRemaining(s -> steps.add(s.toString()));
            return steps;
        }
Maps in the JVM can have {@link Object} as a key, but in JSON they must be a {@link String}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/graphson/GraphSONSerializersV1.java