Don't send whitespace-only assistant message back to Bedrock

pydantic_ai_slim/pydantic_ai/models/bedrock.py

@@ -366,6 +366,22 @@ def _map_inference_config(
 
         return inference_config
 
+    def _map_model_response(self, message: ModelResponse) -> list[ContentBlockOutputTypeDef]:
+        """Maps a `pydantic_ai.ModelResponse` to the Bedrock `ContentBlockOutputTypeDef`.
+
+        This is used to map the model response to the Bedrock format.
+        """
+        content: list[ContentBlockOutputTypeDef] = []
+        for item in message.parts:
+            if isinstance(item, TextPart):
+                if not item.content.strip():
+                    continue
+                content.append({'text': item.content})
+            else:
+                assert isinstance(item, ToolCallPart)
+                content.append(self._map_tool_call(item))
+        return content
+
     async def _map_messages(
         self, messages: list[ModelMessage]
     ) -> tuple[list[SystemContentBlockTypeDef], list[MessageUnionTypeDef]]:
@@ -420,13 +436,7 @@ async def _map_messages(
                                 }
                             )
             elif isinstance(message, ModelResponse):
-                content: list[ContentBlockOutputTypeDef] = []
-                for item in message.parts:
-                    if isinstance(item, TextPart):
-                        content.append({'text': item.content})
-                    else:
-                        assert isinstance(item, ToolCallPart)
-                        content.append(self._map_tool_call(item))
+                content: list[ContentBlockOutputTypeDef] = self._map_model_response(message)
                 bedrock_messages.append({'role': 'assistant', 'content': content})
             else:
                 assert_never(message)

tests/models/test_bedrock.py

@@ -629,3 +629,60 @@ async def test_bedrock_group_consecutive_tool_return_parts(bedrock_provider: Bed
             },
         ]
     )
+
+
+async def test_bedrock_handles_empty_content_blocks(bedrock_provider: BedrockProvider):
+    """
+    Test that the Bedrock provider correctly handles empty content blocks without errors.
+    This test verifies that empty content in UserPromptPart, TextPart, and ToolReturnPart
+    are processed properly without causing issues.
+    """
+    model = BedrockConverseModel('us.amazon.nova-micro-v1:0', provider=bedrock_provider)
+    now = datetime.datetime.now()
+
+    req = [
+        ModelRequest(parts=[UserPromptPart(content=['Please use the tool'])]),
+        ModelResponse(
+            parts=[
+                TextPart(content=""" """),
+                ToolCallPart(
+                    tool_name='normal_tool',
+                    args={'param': 'value'},
+                    tool_call_id='normal1',
+                ),
+            ]
+        ),
+        ModelRequest(
+            parts=[
+                ToolReturnPart(tool_name='normal_tool', content='result', tool_call_id='normal1', timestamp=now),
+            ]
+        ),
+    ]
+
+    _, bedrock_messages = await model._map_messages(req)  # type: ignore[reportPrivateUsage]
+
+    assert bedrock_messages == snapshot(
+        [
+            {'role': 'user', 'content': [{'text': 'Please use the tool'}]},
+            {
+                'role': 'assistant',
+                'content': [
+                    {
+                        'toolUse': {
+                            'input': {
+                                'param': 'value',
+                            },
+                            'name': 'normal_tool',
+                            'toolUseId': 'normal1',
+                        },
+                    },
+                ],
+            },
+            {
+                'role': 'user',
+                'content': [
+                    {'toolResult': {'toolUseId': 'normal1', 'content': [{'text': 'result'}], 'status': 'success'}}
+                ],
+            },
+        ]
+    )