arrow-arith is_null is buggy with NullArray #4565
Description
Describe the bug
When using the arith kernel's is_null or is_not_null on arrays of type NullArray (with datatype Null) the .nulls() buffer is always empty for these types. Therefor the kernel returns an array with all values false/true which is the exact opposite of what should be returned.
To Reproduce
Noticed it here apache/datafusion#7038
Run this unit test in datafusion/is_null.rs
fn is_null_op_allnull() -> Result<()> {
let schema = Schema::new(vec![Field::new("a", DataType::Null, true)]);
let mut a = NullBuilder::with_capacity(1);
// expression: "a is null"
let expr = is_null(col("a", &schema)?).unwrap();
let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(a.finish())])?;
let result = expr.evaluate(&batch)?.into_array(batch.num_rows());
let result =
as_boolean_array(&result).expect("failed to downcast to BooleanArray");
let expected = &BooleanArray::from(vec![true]);
assert_eq!(expected, result);
Ok(())
}
Expected behavior
for is_null I expect a BoolArray of true values for NullArray input (irrespective of length).
for is_not_null I expect a BoolArray of false values for NullArray input (irrespective of length).
Additional context