diff --git a/backend/open_webui/utils/anthropic.py b/backend/open_webui/utils/anthropic.py
index 5f1498c0f1..f0d49d8578 100644
--- a/backend/open_webui/utils/anthropic.py
+++ b/backend/open_webui/utils/anthropic.py
@@ -364,7 +364,7 @@ def convert_anthropic_payload_to_chat_completions(
                 if openai_content:
                     msg_dict['content'] = _finalize_chat_completions_content(openai_content)
                 else:
-                    msg_dict['content'] = ''
+                    msg_dict['content'] = None
                 msg_dict['tool_calls'] = tool_calls
                 messages.append(msg_dict)
             elif openai_content or role == 'assistant':
diff --git a/backend/open_webui/utils/memory.py b/backend/open_webui/utils/memory.py
index 11e405c1a9..e27bf69d4e 100644
--- a/backend/open_webui/utils/memory.py
+++ b/backend/open_webui/utils/memory.py
@@ -500,7 +500,7 @@ async def _review_memory(
         role = message.get('role', '')
         content = message.get('content', '')
         if not isinstance(content, str):
-            content = get_content_from_message(message)
+            content = get_content_from_message(message) or ''
         content = content.strip()
         if role not in {'user', 'assistant'} or not content:
             continue
diff --git a/backend/open_webui/utils/middleware.py b/backend/open_webui/utils/middleware.py
index 26293e95a3..82e7aef1c6 100644
--- a/backend/open_webui/utils/middleware.py
+++ b/backend/open_webui/utils/middleware.py
@@ -1029,7 +1029,7 @@ async def chat_completion_tools_handler(
 
         recent_messages = messages[-4:] if len(messages) > 4 else messages
         chat_history = '\n'.join(
-            f'{message["role"].upper()}: """{get_content_from_message(message)}"""' for message in recent_messages
+            f'{message["role"].upper()}: """{get_content_from_message(message) or ""}"""' for message in recent_messages
         )
 
         prompt = f'History:\n{chat_history}\nQuery: {user_message}' if chat_history else f'Query: {user_message}'
diff --git a/backend/open_webui/utils/misc.py b/backend/open_webui/utils/misc.py
index 25561c0f5b..7cea189b9e 100644
--- a/backend/open_webui/utils/misc.py
+++ b/backend/open_webui/utils/misc.py
@@ -223,7 +223,7 @@ def get_message_list(messages_map, message_id):
 
 
 def get_messages_content(messages: list[dict]) -> str:
-    return '\n'.join([f'{message["role"].upper()}: {get_content_from_message(message)}' for message in messages])
+    return '\n'.join([f'{message["role"].upper()}: {get_content_from_message(message) or ""}' for message in messages])
 
 
 def get_last_user_message_item(messages: list[dict]) -> dict | None:
@@ -477,7 +477,7 @@ def convert_output_to_messages(
 
         message = {
             'role': 'assistant',
-            'content': '\n'.join(pending_content) if pending_content else '',
+            'content': '\n'.join(pending_content) if pending_content else (None if pending_tool_calls else ''),
             **({'tool_calls': pending_tool_calls} if pending_tool_calls else {}),
         }