bjchambers commented on issue #734:
URL: https://github.com/apache/arrow-rs/issues/734#issuecomment-910492451
```
#[test]
fn test_null_struct() {
let struct_type =
DataType::Struct(vec![Field::new("data", DataType::Int64,
true)]);
let array = new_null_array(&struct_type, 9);
let a = array.as_any().downcast_ref::<StructArray>().unwrap();
assert_eq!(a.len(), 9);
for i in 0..9 {
assert!(a.is_null(i));
}
// assert_eq!(a.column(0).len(), 9); // fails (length is 0)
// a.slice(0, 5); // panics (because the field arrays are empty)
}
```
I see two ways of fixing this:
1. I'm guessing the right way is to have the `new_null_array` create null
columns of the given length for each of the fields.
2. An alternative, could be to *allow* empty columns in the case of an all
null-array. This would allow avoiding the allocation. But... I don't think this
is supported elsewhere, and seems like an extensive change. Hence, I'm guessing
the first is the right solution.
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