DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT doesn't work

[hassomehide]

Empty Strings are not deserialized into null objects, even if ACCEPT_EMPTY_STRING_AS_NULL_OBJECT is enabled. Sample code is here:

ObjectReader:

private ObjectReader getObjectReader() {
  CsvMapper mapper = new CsvMapper();
  mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
  CsvSchema schema = mapper.schema().withHeader().withColumnSeparator(';');
  return mapper.reader(schema).forType(TestRow.class);
}

Object:

private static class TestRow {
  private String testString;
  private Integer testInteger;
  private Float testFloat;
  private TestEnum testEnum;

  // getters/setters
}

CSV file (first row is the header, second row is the data):

testString;testInteger;testFloat;testEnum
;;;

Test case:

@Test
public void testNulls() throws IOException {
  // map from CSV to TestRow
  assertNull(row.getTestInteger()); // succeeds
  assertNull(row.getTestFloat()); // succeeds
  assertNull(row.getTestEnum()); // succeeds
  assertNull(row.getTestString()); // fails
}

[cowtowncoder]

I assume what you get here is an exception for last case?

[hassomehide]

An AssertionError, because the value of testString is "", no matter if ACCEPT_EMPTY_STRING_AS_NULL_OBJECT is enabled or not.

[cowtowncoder]

Ok, I don't think that is an error, then. String in context of Jackson is considered a scalar type, and not Object in that sense -- I realize it is java.lang.Object, but within Jackson terminology it is not Object. Feature should be named ACCEPT_EMPTY_STRINGS_AS_NULL_POJO to reflect this.

However; for CSV handling specifically it would be possible to add separate CsvParser.Feature to force coercion from Empty String into null. If this isn't already the case

[cowtowncoder]

Actually: come to think of this, there is already a mechanism for this: when constructing CsvSchema, use withNullValue("") to specify that empty String should be read as Java null. This works for columns of all types.

[hassomehide]

Right, this works. Thanks!

[robmoore]

I'm already using withNullValue() for NULL so I was hoping that the DeserializationFeature approach would work in conjunction with the withNullValue() setting. Any chance that withNullValues() might be added to support multiple items?

[cowtowncoder]

@robmoore I am hesitant to add support for a larger set of transformations. But if it'd be enough to just support empty String and one alternative notation (like "null"), I think that this combination should work (or be made to work if not yet) -- coercion of "" to null Object / default scalar value is something jackson-databind supports.

But I think you may want to file a separate issue for your specific use case, partly since this issue is closed, and partly since your usage/expectation may be slightly different.
This would be good time to file a new issue, too, as I am hoping to complete 2.9.0.pr2 and in particular trying to decide what incremental improvements could still be made in CSV module.

[robmoore]

@cowtowncoder The solution you propose would work fine for this use case. I'll open a separate ticket.