fix take on empty struct array (#7224)

Author: westonpace

arrow-select/src/take.rs

@@ -254,7 +254,12 @@ fn take_impl<IndexType: ArrowPrimitiveType>(
                 })
                 .collect();
 
-            Ok(Arc::new(StructArray::from((fields, is_valid))) as ArrayRef)
+            if fields.is_empty() {
+                let nulls = NullBuffer::new(BooleanBuffer::new(is_valid, 0, indices.len()));
+                Ok(Arc::new(StructArray::new_empty_fields(indices.len(), Some(nulls))))
+            } else {
+                Ok(Arc::new(StructArray::from((fields, is_valid))) as ArrayRef)
+            }
         }
         DataType::Dictionary(_, _) => downcast_dictionary_array! {
             values => Ok(Arc::new(take_dict(values, indices)?)),
@@ -1968,6 +1973,15 @@ mod tests {
         ]);
 
         assert_eq!(&expected, actual);
+
+        let nulls = NullBuffer::from(&[false, true, false, true, false, true]);
+        let empty_struct_arr = StructArray::new_empty_fields(6, Some(nulls));
+        let index = UInt32Array::from(vec![0, 2, 1, 4]);
+        let actual = take(&empty_struct_arr, &index, None).unwrap();
+
+        let expected_nulls = NullBuffer::from(&[false, false, true, false]);
+        let expected_struct_arr = StructArray::new_empty_fields(4, Some(expected_nulls));
+        assert_eq!(&expected_struct_arr, actual.as_struct());
     }
 
     #[test]