@Test
  void undefined() throws IOException {
    JsonParser parser = Parsers.parserAt(new BsonUndefined());
    check(parser.currentToken()).is(JsonToken.VALUE_NULL);
    check(parser.getText()).is(JsonToken.VALUE_NULL.asString());
    parser.nextToken();
  }
Validate different type conversions like {@code DateTime => Long => String}
criteria/mongo/test/org/immutables/criteria/mongo/bson4jackson/TypeConversionTest.java