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[BUG]: Nested nulls can be interpreted at the wrong level

See original GitHub issue

Library Version

4.6.1

OS

Linux

OS Architecture

64 bit

How to reproduce?

I’m encountering problems with serialization of nested null values. Results of serialization->deserialiation can interpret the null at the wrong level.

I encountered issues working with the Table API with nested arrays, but when I tried to put together a minimal breaking example, I found this relatively simple case that leads to failure with the Class API, without arrays.

Failing test

Try this test in ParquetSerializerTest.cs:

        [Fact]
        public async Task Struct_Serde_With_NestedNulls() {

            var data = new List<AddressBookEntry> {
                new AddressBookEntry {
                    FirstName = "Joe",
                    LastName = "Bloggs",
                    Address = new Address() {
                        City = null,
                        Country = null
                    }
                }
            };

            using var ms = new MemoryStream();
            await ParquetSerializer.SerializeAsync(data, ms);

            ms.Position = 0;
            IList<AddressBookEntry> data2 = await ParquetSerializer.DeserializeAsync<AddressBookEntry>(ms);

            Assert.Equivalent(data2, data);
        }

This tests should succeed, but it fails with

[xUnit.net 00:00:01.16]     Parquet.Test.Serialisation.ParquetSerializerTest.Struct_Serde_With_NestedNulls [FAIL]
  Failed Parquet.Test.Serialisation.ParquetSerializerTest.Struct_Serde_With_NestedNulls [269 ms]
  Error Message:
   Assert.Equivalent() Failure: Collection value not found
Expected: AddressBookEntry { Address = null, FirstName = "Joe", LastName = "Bloggs" }
In:       [AddressBookEntry { Address = Address { ... }, FirstName = "Joe", LastName = "Bloggs" }]
  Stack Trace:
     at Parquet.Test.Serialisation.ParquetSerializerTest.Struct_Serde_With_NestedNulls() in /tmp/parquet-dotnet/src/Parquet.Test/Serialisation/ParquetSerializerTest.cs:line 118
--- End of stack trace from previous location ---

Failed!  - Failed:     1, Passed:     0, Skipped:     0, Total:     1, Duration: < 1 ms - Parquet.Test.dll (net7.0)