Check `return_code` is `None` during job running

run_jobs.py

@@ -161,7 +161,7 @@ def pop_job_from_pipe():
     with open(f"./tmp/{task_id}.log", "a") as log_file:
         return_code = None
         p = subprocess.Popen(command, stdout=log_file, stderr=subprocess.STDOUT)
-        while pipe.current and not return_code:
+        while pipe.current and return_code is None:
             # Wait for finishing
             try:
                 return_code = p.wait(timeout=1)