diff --git a/plugins/platforms/slack/adapter.py b/plugins/platforms/slack/adapter.py
index 1a03c2b57f22..90fbcdc7da38 100644
--- a/plugins/platforms/slack/adapter.py
+++ b/plugins/platforms/slack/adapter.py
@@ -3820,7 +3820,7 @@ class SlackAdapter(BasePlatformAdapter):
                     team_id=team_id,
                     strip_bot_mention=False,
                 )
-                if f"<@{bot_uid}>" in parent_text:
+                if parent_text and f"<@{bot_uid}>" in parent_text:
                     # Remember the thread so later replies skip the fetch.
                     if not self._slack_strict_mention():
                         self._register_mentioned_thread(event_thread_ts)
diff --git a/tests/gateway/test_slack.py b/tests/gateway/test_slack.py
index cd121c313abf..ac67760f41c3 100644
--- a/tests/gateway/test_slack.py
+++ b/tests/gateway/test_slack.py
@@ -3538,8 +3538,6 @@ class TestThreadReplyHandling:
         a._bot_user_id = "U_BOT"
         a._team_bot_user_ids = {"T_TEAM": "U_BOT"}
         a._running = True
-        a._fetch_thread_parent_text = AsyncMock(return_value=None)
-        a._fetch_thread_context = AsyncMock(return_value="")
         a.handle_message = AsyncMock()
         a.set_session_store(mock_session_store)
         return a
@@ -3924,8 +3922,6 @@ class TestAssistantThreadLifecycle:
         a._bot_user_id = "U_BOT"
         a._team_bot_user_ids = {"T_TEAM": "U_BOT"}
         a._running = True
-        a._fetch_thread_parent_text = AsyncMock(return_value=None)
-        a._fetch_thread_context = AsyncMock(return_value="")
         a.handle_message = AsyncMock()
         a.set_session_store(mock_session_store)
         return a