From 46ef407dab273465fedf2849777f66370a9eac6f Mon Sep 17 00:00:00 2001
From: Your Name <jonathan.f.hill@gmail.com>
Date: Sun, 17 May 2026 13:51:07 -0500
Subject: [PATCH 1/2] fix: guard against IndexError on empty LLM
 choices/content list
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Three call sites access choices[0] or content[0] without checking
whether the API returned any results — content-policy filters, token
limits, and rate-limit fallbacks can all return an empty list.

- api_provider.py: early return when res.choices is empty
- classify/label.py: skip iteration when completion.choices is empty
- classify/label.py: skip Anthropic iteration when response.content is empty
- criteria_labeling.py: skip iteration when completion.choices is empty
---
 fastchat/serve/api_provider.py              | 2 ++
 fastchat/serve/monitor/classify/label.py    | 4 ++++
 fastchat/serve/monitor/criteria_labeling.py | 2 ++
 3 files changed, 8 insertions(+)

diff --git a/fastchat/serve/api_provider.py b/fastchat/serve/api_provider.py
index 2e967e3ef..817275321 100644
--- a/fastchat/serve/api_provider.py
+++ b/fastchat/serve/api_provider.py
@@ -348,6 +348,8 @@ def openai_api_stream_iter(
                 max_tokens=max_new_tokens,
                 stream=False,
             )
+        if not res.choices:
+            return
         text = res.choices[0].message.content
         pos = 0
         while pos < len(text):
diff --git a/fastchat/serve/monitor/classify/label.py b/fastchat/serve/monitor/classify/label.py
index fe928a9ba..44b7c1ea4 100644
--- a/fastchat/serve/monitor/classify/label.py
+++ b/fastchat/serve/monitor/classify/label.py
@@ -64,6 +64,8 @@ def chat_completion_openai(model, messages, temperature, max_tokens, api_dict=No
                 max_tokens=max_tokens,
                 # extra_body={"guided_choice": GUIDED_CHOICES} if GUIDED_CHOICES else None,
             )
+            if not completion.choices:
+                break
             output = completion.choices[0].message.content
             # print(output)
             break
@@ -114,6 +116,8 @@ def chat_completion_anthropic(model, messages, temperature, max_tokens, api_dict
                 temperature=temperature,
                 system=sys_msg,
             )
+            if not response.content:
+                break
             output = response.content[0].text
             break
         except anthropic.APIError as e:
diff --git a/fastchat/serve/monitor/criteria_labeling.py b/fastchat/serve/monitor/criteria_labeling.py
index b08b030d4..bb601bda3 100644
--- a/fastchat/serve/monitor/criteria_labeling.py
+++ b/fastchat/serve/monitor/criteria_labeling.py
@@ -89,6 +89,8 @@ def chat_completion_openai(model, messages, temperature, max_tokens, api_dict=No
                 max_tokens=max_tokens,
                 # extra_body={"guided_choice": GUIDED_CHOICES} if GUIDED_CHOICES else None,
             )
+            if not completion.choices:
+                break
             output = completion.choices[0].message.content
             break
         except openai.RateLimitError as e:

From cab948d902e4a88b060def44e6c264435cd866dc Mon Sep 17 00:00:00 2001
From: Your Name <jonathan.f.hill@gmail.com>
Date: Sun, 17 May 2026 17:00:50 -0500
Subject: [PATCH 2/2] fix: extend guards to cover choices[0].message is None
 (Gemini content-filter)

Gemini 2.5 Flash returns HTTP 200 with choices[0].message=None when content
is filtered (finish_reason: PROHIBITED_CONTENT), causing AttributeError even
when choices is non-empty. Extends all three guards from `if not choices:`
to `if not choices or choices[0].message is None:`.
---
 fastchat/serve/api_provider.py              | 2 +-
 fastchat/serve/monitor/classify/label.py    | 2 +-
 fastchat/serve/monitor/criteria_labeling.py | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fastchat/serve/api_provider.py b/fastchat/serve/api_provider.py
index 817275321..dc15c82a6 100644
--- a/fastchat/serve/api_provider.py
+++ b/fastchat/serve/api_provider.py
@@ -348,7 +348,7 @@ def openai_api_stream_iter(
                 max_tokens=max_new_tokens,
                 stream=False,
             )
-        if not res.choices:
+        if not res.choices or res.choices[0].message is None:
             return
         text = res.choices[0].message.content
         pos = 0
diff --git a/fastchat/serve/monitor/classify/label.py b/fastchat/serve/monitor/classify/label.py
index 44b7c1ea4..925167f81 100644
--- a/fastchat/serve/monitor/classify/label.py
+++ b/fastchat/serve/monitor/classify/label.py
@@ -64,7 +64,7 @@ def chat_completion_openai(model, messages, temperature, max_tokens, api_dict=No
                 max_tokens=max_tokens,
                 # extra_body={"guided_choice": GUIDED_CHOICES} if GUIDED_CHOICES else None,
             )
-            if not completion.choices:
+            if not completion.choices or completion.choices[0].message is None:
                 break
             output = completion.choices[0].message.content
             # print(output)
diff --git a/fastchat/serve/monitor/criteria_labeling.py b/fastchat/serve/monitor/criteria_labeling.py
index bb601bda3..75010a563 100644
--- a/fastchat/serve/monitor/criteria_labeling.py
+++ b/fastchat/serve/monitor/criteria_labeling.py
@@ -89,7 +89,7 @@ def chat_completion_openai(model, messages, temperature, max_tokens, api_dict=No
                 max_tokens=max_tokens,
                 # extra_body={"guided_choice": GUIDED_CHOICES} if GUIDED_CHOICES else None,
             )
-            if not completion.choices:
+            if not completion.choices or completion.choices[0].message is None:
                 break
             output = completion.choices[0].message.content
             break