fix: Properly handle prompt=None & avoid agent hanging

pyproject.toml

@@ -234,8 +234,8 @@ test-integ = [
     "hatch test tests_integ {args}"
 ]
 prepare = [
-    "hatch fmt --linter",
     "hatch fmt --formatter",
+    "hatch fmt --linter",
     "hatch run test-lint",
     "hatch test --all"
 ]

src/strands/models/bedrock.py

@@ -418,14 +418,14 @@ def _stream(
             ContextWindowOverflowException: If the input exceeds the model's context window.
             ModelThrottledException: If the model service is throttling requests.
         """
-        logger.debug("formatting request")
-        request = self.format_request(messages, tool_specs, system_prompt)
-        logger.debug("request=<%s>", request)
+        try:
+            logger.debug("formatting request")
+            request = self.format_request(messages, tool_specs, system_prompt)
+            logger.debug("request=<%s>", request)
 
-        logger.debug("invoking model")
-        streaming = self.config.get("streaming", True)
+            logger.debug("invoking model")
+            streaming = self.config.get("streaming", True)
 
-        try:
             logger.debug("got response from model")
             if streaming:
                 response = self.client.converse_stream(**request)

tests/strands/models/test_bedrock.py

@@ -419,6 +419,15 @@ async def test_stream_throttling_exception_from_event_stream_error(bedrock_clien
     )
 
 
+@pytest.mark.asyncio
+async def test_stream_with_invalid_content_throws(bedrock_client, model, alist):
+    # We used to hang on None, so ensure we don't regress: https://github.com/strands-agents/sdk-python/issues/642
+    messages = [{"role": "user", "content": None}]
+
+    with pytest.raises(TypeError):
+        await alist(model.stream(messages))
+
+
 @pytest.mark.asyncio
 async def test_stream_throttling_exception_from_general_exception(bedrock_client, model, messages, alist):
     error_message = "ThrottlingException: Rate exceeded for ConverseStream"