Filter has inconsistent null handling

[ritchie46]

Describe the bug
When creating a boolean mask from a comparison operation on an array with null values, the filter kernel yields a different result than when that boolean mask, including null values, is created directly.

To Reproduce

    fn test_null_mask() -> Result<()> {
        use crate::compute::kernels::comparison;
        let a: PrimitiveArray<Int64Type> = PrimitiveArray::from(vec![Some(1), Some(2), None]);
        let mask0 = comparison::eq(&a, &a)?;
        let out0 = filter(&a, &mask0)?;
        let out_arr0 = out0.as_any().downcast_ref::<PrimitiveArray<Int64Type>>().unwrap();

        let mask1 = BooleanArray::from(vec![Some(true), Some(true), None]);
        let out1 = filter(&a, &mask1)?;
        let out_arr1 = out1.as_any().downcast_ref::<PrimitiveArray<Int64Type>>().unwrap();
        assert_eq!(mask0, mask1); // assert succes
        assert_eq!(out_arr0, out_arr1);  // assert false
        Ok(())
    }

Expected behavior
Null values in the predicate mask should be ignored and not yield a result. Which the kernel does correctly on boolean mask that are created directly.