[Rust][Arrow] Nulls are transformed into "" after filtering for StringArray

[asfimport]

When I use the filter kernel with Null strings, any input column that was Null turns into an empty string after filtering.

For example, this test (in filter.rs) should pass:

    #[test]
    fn test_filter_string_array_with_null() {
        let a = StringArray::from(vec![Some("hello"), None, Some("world"), None]);
        let b = BooleanArray::from(vec![true, false, false, true]);
        let c = filter(&a, &b).unwrap();
        let d = c.as_ref().as_any().downcast_ref::<StringArray>().unwrap();
        assert_eq!(2, d.len());
        assert_eq!("hello", d.value(0));
        assert_eq!(true, d.is_null(1));
    }

But instead it fails (the second element in the output array should be null )

---- compute::kernels::filter::tests::test_filter_string_array_with_null stdout ----
thread 'compute::kernels::filter::tests::test_filter_string_array_with_null' panicked at 'assertion failed: `(left == right)`
  left: `true`,
 right: `false`', arrow/src/compute/kernels/filter.rs:686:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Reporter: Andrew Lamb / @alamb
Assignee: Andrew Lamb / @alamb

Related issues:

• [Rust] BinaryArray filter replaces nulls with empty strings (is duplicated by)

PRs and other links:

• GitHub Pull Request #8303

_{Note: This issue was originally created as ARROW-10136. Please see the migration documentation for further details.}

[asfimport]

Andy Grove / @andygrove:
Issue resolved by pull request 8303
#8303