crepererum opened a new issue #306:
URL: https://github.com/apache/arrow-rs/issues/306
**Describe the bug**
When serializing an all-null arrow array to parquet, the null-count in the
stats is always 0.
**To Reproduce**
Steps to reproduce the behavior:
```rust
#[test]
fn statistics_null_counts_only_nulls() {
// check that null-count statistics for "only NULL"-columns are correct
let values = Arc::new(UInt64Array::from(vec![
None,
None,
]));
let file = one_column_roundtrip("null_counts", values, true);
// check statistics are valid
let reader = SerializedFileReader::new(file).unwrap();
let metadata = reader.metadata();
assert_eq!(metadata.num_row_groups(), 1);
let row_group = metadata.row_group(0);
assert_eq!(row_group.num_columns(), 1);
let column = row_group.column(0);
let stats = column.statistics().unwrap();
assert_eq!(stats.null_count(), 2); // <<< this fails, null count is 0
}
```
**Expected behavior**
For all-null columns the null-count should be the same as the number of rows.
**Additional context**
Tested on `c863a2c44bffa5c092a49e07910d5e9225483193`.
**I am claiming this issue since I have a fix ready.**
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