Lint files

Author: Saul Cooperman

src/pystack/traceback_formatter.py

@@ -25,7 +25,7 @@ def print_thread(self, thread: PyThread) -> None:
         if self.include_subinterpreters:
             if thread.interpreter_id != self._current_interpreter_id:
                 self._print_interpreter_header(thread.interpreter_id)
-                self._current_interpreter_id = thread.interpreter_id
+                self._current_interpreter_id = thread.interpreter_id or -1
 
         # Print the thread with indentation
         for line in format_thread(thread, self.native_mode):