From 1f573d048f0c2c33eb5a56a61e9864b6978ea910 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?d=20=F0=9F=94=B9?=
 <258577966+voidborne-d@users.noreply.github.com>
Date: Sat, 21 Mar 2026 12:09:48 +0000
Subject: [PATCH] fix: copy dict before mutation + use filter(None, ...) to
 avoid trailing space

Address review feedback:
- Shallow-copy next_m before mutating to avoid side-effects on caller's dict
- Use ' '.join(filter(None, ...)) to prevent trailing space when next_text is empty
---
 litellm/litellm_core_utils/prompt_templates/factory.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/litellm/litellm_core_utils/prompt_templates/factory.py b/litellm/litellm_core_utils/prompt_templates/factory.py
index 99be6d02e2c..2f0678cf0fc 100644
--- a/litellm/litellm_core_utils/prompt_templates/factory.py
+++ b/litellm/litellm_core_utils/prompt_templates/factory.py
@@ -119,8 +119,12 @@ def map_system_message_pt(messages: list) -> list:
                     next_role == "user" or next_role == "assistant"
                 ):  # Next message is a user or assistant message
                     # Merge system prompt into the next message
+                    # Copy to avoid mutating the caller's original dict
+                    next_m = messages[i + 1] = {**next_m}
                     next_text = _get_content_as_str(next_m["content"])
-                    next_m["content"] = system_text + " " + next_text
+                    next_m["content"] = " ".join(
+                        filter(None, [system_text, next_text])
+                    )
                 elif next_role == "system":  # Next message is a system message
                     # Append a user message instead of the system message
                     new_message = {"role": "user", "content": system_text}