fix(models): skip empty text parts in Anthropic message conversion

src/google/adk/models/anthropic_llm.py

@@ -336,6 +336,16 @@ def _is_pdf_part(part: types.Part) -> bool:
   )
 
 
+def _is_empty_text_part(part: types.Part) -> bool:
+  """Returns True for parts that carry nothing but an empty text string.
+
+  ADK itself can produce such parts (e.g. code execution with no output writes
+  `Part(text='')` into the content), and Anthropic rejects empty text blocks.
+  """
+  payload = part.model_dump(exclude_none=True)
+  return payload.get("text") == "" and set(payload) <= {"text", "thought"}
+
+
 def _normalize_image_media_type(mime_type: str) -> _ImageMediaType:
   normalized = mime_type.split(";", 1)[0].strip().lower()
   if normalized not in _ANTHROPIC_IMAGE_MEDIA_TYPES:
@@ -575,6 +585,12 @@ def _content_to_message_param(
       logger.warning("PDF data is not supported in Claude for assistant turns.")
       continue
 
+    # Anthropic rejects empty text blocks; skip them rather than failing the
+    # whole request with NotImplementedError.
+    if _is_empty_text_part(part):
+      logger.debug("Skipping empty text part for Claude request.")
+      continue
+
     message_block.append(_part_to_message_block(part, sanitizer))
 
   return {

tests/unittests/models/test_anthropic_llm.py

@@ -1080,6 +1080,38 @@ def test_content_to_message_param(
 # --- Tests for Bug #2: json.dumps for dict/list function results ---
 
 
+def test_content_to_message_param_skips_empty_text_part():
+  """An empty text part must be skipped instead of raising NotImplementedError.
+
+  ADK can emit `Part(text='')` itself, e.g. when code execution produces no
+  output, and Anthropic rejects empty text blocks.
+  """
+  content = types.Content(
+      role="user",
+      parts=[
+          types.Part(text="run it"),
+          types.Part(text=""),
+      ],
+  )
+
+  result = content_to_message_param(content)
+
+  assert result["role"] == "user"
+  assert result["content"] == [{"type": "text", "text": "run it"}]
+
+
+def test_content_to_message_param_keeps_non_text_payload_with_empty_text():
+  """A part that has other payload alongside empty text is not dropped."""
+  part = types.Part(text="")
+  part.function_call = types.FunctionCall(id="call_1", name="tool", args={})
+  content = types.Content(role="model", parts=[part])
+
+  result = content_to_message_param(content)
+
+  assert len(result["content"]) == 1
+  assert result["content"][0]["type"] == "tool_use"
+
+
 def test_part_to_message_block_dict_result_serialized_as_json():
   """Dict results should be serialized with json.dumps, not str()."""
   response_part = types.Part.from_function_response(