presto-mongodb/src/main/java/io/prestosql/plugin/mongodb/MongoPageSource.java/MongoPageSource/toVarcharValue
class MongoPageSource:    private String toVarcharValue(Object value)
    {
        if (value instanceof Collection<?>) {
            return "[" + join(", ", ((Collection<?>) value).stream().map(this::toVarcharValue).collect(toList())) + "]";
        }
        if (value instanceof Document) {
            return ((Document) value).toJson();
        }
        return String.valueOf(value);
    }