2023/12/15

That

Any value in an array may be semantically null, whether primitive or nested type.

[…]

Arrays having a 0 null count may choose to not allocate the validity bitmap; how this is represented depends on the implementation

– https://arrow.apache.org/docs/format/Columnar.html#null-count

Which is frustrating. I usually think of arrays or database columns as NOT NULL by default, so I’m disappointed that I need to watch out for that footgun again when writing in-memory DBs.