fix: avro_to_arrow: Handle avro nested nullable struct (union)

Corrects handling of a nullable struct union.

Signed-off-by: 🐼 Samrose Ahmed 🐼 <[email protected]>

Author: Samrose-Ahmed

datafusion/core/src/datasource/avro_to_arrow/arrow_array_reader.rs

@@ -766,14 +766,20 @@ impl<'a, R: Read> AvroArrowArrayReader<'a, R> {
                         let len = rows.len();
                         let num_bytes = bit_util::ceil(len, 8);
                         let mut null_buffer = MutableBuffer::from_len_zeroed(num_bytes);
+                        let empty_vec = vec![];
                         let struct_rows = rows
                             .iter()
                             .enumerate()
                             .map(|(i, row)| (i, self.field_lookup(field.name(), row)))
                             .map(|(i, v)| {
+                                let v = v.map(maybe_resolve_union);
                                 if let Some(Value::Record(value)) = v {
                                     bit_util::set_bit(&mut null_buffer, i);
                                     value
+                                } else if v.is_none() {
+                                    &empty_vec
+                                } else if let Some(Value::Null) = v {
+                                    &empty_vec
                                 } else {
                                     panic!("expected struct got {v:?}");
                                 }