@Override
    public Object visitStringNullableLiteral(final GremlinParser.StringNullableLiteralContext ctx) {
        if (ctx.K_NULL() != null)
            return null;
        else
            return StringEscapeUtils.unescapeJava(stripQuotes(ctx.getText()));
    }
{@inheritDoc}
Generic literal collection returns a list of {@code Object}
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/GenericLiteralVisitor.java