anthropic: ensure that we never send empty text content to the API (#718

)

* anthropic: ensure that we never send empty text content to the API

* Update src/inspect_ai/model/_providers/anthropic.py

Co-authored-by: sdtblckgov <168540866+sdtblckgov@users.noreply.github.com>

---------

Co-authored-by: aisi-inspect <166920645+aisi-inspect@users.noreply.github.com>
Co-authored-by: sdtblckgov <168540866+sdtblckgov@users.noreply.github.com>

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Cleanup Docker Containers immediately for samples with errors.
 - Anthropic: remove stock tool use chain of thought prompt (many Anthropic models now do this internally, in other cases its better for this to be explicit rather than implicit).
+- Anthropic: ensure that we never send empty text content to the API.
 - Google: compatibility with google-generativeai v0.8.3
 - Llama: remove extraneous <|start_header_id|>assistant<|end_header_id|> if it appears in an assistant message.
 - Requirements: require semver>=3.0.0

src/inspect_ai/model/_providers/anthropic.py

@@ -392,6 +392,11 @@ def message_tool_choice(tool_choice: ToolChoice) -> message_create_params.ToolCh
         return {"type": "auto"}
 
 
+# text we insert when there is no content passed
+# (as this will result in an Anthropic API error)
+NO_CONTENT = "(no content)"
+
+
 async def message_param(message: ChatMessage) -> MessageParam:
     # no system role for anthropic (this is more like an assertion,
     # as these should have already been filtered out)
@@ -412,7 +417,7 @@ async def message_param(message: ChatMessage) -> MessageParam:
             if not content:
                 content = "error"
         elif isinstance(message.content, str):
-            content = [TextBlockParam(type="text", text=message.content)]
+            content = [TextBlockParam(type="text", text=message.content or NO_CONTENT)]
         else:
             content = [
                 await message_param_content(content) for content in message.content
@@ -465,7 +470,7 @@ async def message_param(message: ChatMessage) -> MessageParam:
 
     # normal text content
     elif isinstance(message.content, str):
-        return MessageParam(role=message.role, content=message.content)
+        return MessageParam(role=message.role, content=message.content or NO_CONTENT)
 
     # mixed text/images
     else:
@@ -561,7 +566,7 @@ async def message_param_content(
     content: Content,
 ) -> TextBlockParam | ImageBlockParam:
     if isinstance(content, ContentText):
-        return TextBlockParam(type="text", text=content.text)
+        return TextBlockParam(type="text", text=content.text or NO_CONTENT)
     else:
         # resolve to url
         image = content.image