diff --git a/src/agentscope/_version.py b/src/agentscope/_version.py
index 15bac20c90..2a3386b3ef 100644
--- a/src/agentscope/_version.py
+++ b/src/agentscope/_version.py
@@ -1,4 +1,4 @@
 # -*- coding: utf-8 -*-
 """The version of agentscope."""
 
-__version__ = "1.0.19.post1"
+__version__ = "1.0.20"
diff --git a/src/agentscope/formatter/_deepseek_formatter.py b/src/agentscope/formatter/_deepseek_formatter.py
index f9dce39536..5a3d397be6 100644
--- a/src/agentscope/formatter/_deepseek_formatter.py
+++ b/src/agentscope/formatter/_deepseek_formatter.py
@@ -105,7 +105,7 @@ async def _format(
 
             msg_deepseek = {
                 "role": msg.role,
-                "content": content_msg or None,
+                "content": content_msg or (None if tool_calls else ""),
             }
 
             if reasoning_msg:
diff --git a/src/agentscope/formatter/_formatter_base.py b/src/agentscope/formatter/_formatter_base.py
index 6abb05a99e..b75982315e 100644
--- a/src/agentscope/formatter/_formatter_base.py
+++ b/src/agentscope/formatter/_formatter_base.py
@@ -68,6 +68,9 @@ def convert_tool_result_to_string(
                 second element is the corresponding block.
         """
 
+        if output is None:
+            return "", []
+
         if isinstance(output, str):
             return output, []
 
diff --git a/src/agentscope/formatter/_truncated_formatter_base.py b/src/agentscope/formatter/_truncated_formatter_base.py
index 86d42ad41e..4175181be1 100644
--- a/src/agentscope/formatter/_truncated_formatter_base.py
+++ b/src/agentscope/formatter/_truncated_formatter_base.py
@@ -2,7 +2,6 @@
 """The truncated formatter base class, which allows to truncate the input
 messages."""
 from abc import ABC
-from copy import deepcopy
 from typing import (
     Any,
     Tuple,
@@ -66,7 +65,7 @@ async def format(
         # Check if the input messages are valid
         self.assert_list_of_msgs(msgs)
 
-        msgs = deepcopy(msgs)
+        msgs = list(msgs)
 
         while True:
             formatted_msgs = await self._format(msgs)
diff --git a/src/agentscope/model/_anthropic_model.py b/src/agentscope/model/_anthropic_model.py
index 8c9e9d1deb..9c4e607c80 100644
--- a/src/agentscope/model/_anthropic_model.py
+++ b/src/agentscope/model/_anthropic_model.py
@@ -461,10 +461,13 @@ async def _parse_anthropic_stream_completion_response(
                     # (e.g., DashScope), the input tokens are contained in
                     # events where event.type == "message_delta", so we add
                     # this step to extract the value.
-                    final_input_tokens = getattr(
-                        event.usage,
-                        "input_tokens",
-                        0,
+                    final_input_tokens = (
+                        getattr(
+                            event.usage,
+                            "input_tokens",
+                            0,
+                        )
+                        or 0
                     )
                     if final_input_tokens > usage.input_tokens:
                         usage.input_tokens = final_input_tokens