Update datafusion/functions-aggregate/src/array_agg.rs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: GaneshPatil7517

datafusion/functions-aggregate/src/array_agg.rs

@@ -112,19 +112,19 @@ impl AggregateUDFImpl for ArrayAgg {
     }
 
     fn return_field(&self, arg_fields: &[FieldRef]) -> Result<FieldRef> {
-        // Preserve the nullability of the input field in the list field
-        // If the input is non-nullable, the list itself is non-nullable
-        // If the input is nullable, the list is nullable
+        // Preserve the nullability of the input field in the aggregate result field
+        // If the input is non-nullable, the aggregate result field is non-nullable
+        // If the input is nullable, the aggregate result field is nullable
         let input_field = &arg_fields[0];
         let list_field = Field::new_list_field(
             input_field.data_type().clone(),
-            true, // elements in the list can be null
+            true, // elements in the list (array elements) can be null
         );
 
         Ok(Arc::new(Field::new(
             self.name(),
             DataType::List(Arc::new(list_field)),
-            input_field.is_nullable(), // preserve input field's nullability
+            input_field.is_nullable(), // preserve input field's nullability in the aggregate result field
         )))
     }