`arrow.enable_null_check_for_get` causes change in the behavior of `VarBinaryVector#getObject`

[aqni]

Describe the bug, including details regarding any error messages, version, and platform.

• version: 18.1.0
• platform: windows, jdk17

  @Test
  void testVarbinary(){
    try(RootAllocator allocator = new RootAllocator(Long.MAX_VALUE);
        BigIntVector bigIntVector = new BigIntVector("test", allocator);
        VarBinaryVector varBinVector = new VarBinaryVector("test", allocator)){
      bigIntVector.setNull(0);
      bigIntVector.setValueCount(1);
      varBinVector.setNull(0);
      varBinVector.setValueCount(1);
      Assertions.assertNull(bigIntVector.getObject(0));
      Assertions.assertNull(varBinVector.getObject(0));
    }
  }

When I set arrow.enable_null_check_for_get to true, this test passes. However, when I set arrow.enable_null_check_for_get to false, it failed.

org.opentest4j.AssertionFailedError: 
Expected :null
Actual   :[B@73e9cf30
	at org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
	at org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
	at org.junit.jupiter.api.AssertNull.failNotNull(AssertNull.java:50)
	at org.junit.jupiter.api.AssertNull.assertNull(AssertNull.java:35)
	at org.junit.jupiter.api.AssertNull.assertNull(AssertNull.java:30)
	at org.junit.jupiter.api.Assertions.assertNull(Assertions.java:279)
	at demo.MainTest.testVarbinary(MainTest.java:27)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)

Why does BigIntVector's getObject always return null, while VarBinary Vector's getObject has a different behavior?

[lidavidm]

Because you've disabled null checking entirely, so VarBinaryVector takes it as an opportunity to skip the null check and return whatever string data happens to be in that slot (even though the slot is meant to be null, it can still have data allocated, though it is probably an empty string). BigIntVector doesn't have that optimization.

[lidavidm]

Arguably, in this case, BigIntVector should also be returning non-null.

[aqni]

Is there any plan in the future to unify the behavior of getObject when arrow.enable_null_check_for_get is set to false?

[lidavidm]

Contributions would be welcome. I don't think anyone is actively working on it.