fix: LightevalTaskConfig.stop_sequence attribute (#463)

* fix: LightevalTaskConfig.stop_sequence attribute

* fix: linter

---------

Co-authored-by: Nathan Habib <30601243+NathanHB@users.noreply.github.com>

src/lighteval/tasks/lighteval_task.py

@@ -130,7 +130,7 @@ def __post_init__(self):
         self.hf_avail_splits = tuple(self.hf_avail_splits) if self.hf_avail_splits is not None else None
         self.evaluation_splits = tuple(self.evaluation_splits)
         self.suite = tuple(self.suite)
-        self.stop_sequence = tuple(self.stop_sequence) if self.stop_sequence is not None else None
+        self.stop_sequence = tuple(self.stop_sequence) if self.stop_sequence is not None else ()
 
     def print(self):
         md_writer = MarkdownTableWriter()