fix the handling of unknown part types

Author: gaborfeher

src/a2a/contrib/tasks/vertex_task_converter.py

@@ -107,7 +107,7 @@ def to_sdk_part(stored_part: vertexai_types.Part) -> Part:
             )
         )
 
-    return Part(root=TextPart(text=''))
+    raise ValueError(f"Unsupported part: {stored_part}")
 
 
 def to_stored_artifact(artifact: Artifact) -> vertexai_types.TaskArtifact:

tests/contrib/tasks/test_vertex_task_converter.py

@@ -1,8 +1,8 @@
 import base64
-import json
 
 import pytest
 
+
 pytest.importorskip(
     'vertexai', reason='Vertex Task Converter tests require vertexai'
 )
@@ -190,11 +190,10 @@ def test_to_sdk_part_file_data() -> None:
     assert sdk_part.root.file.uri == 'gs://bucket/image.jpg'
 
 
-def test_to_sdk_part_empty() -> None:
+def test_to_sdk_part_unsupported() -> None:
     stored_part = vertexai_types.Part()
-    sdk_part = to_sdk_part(stored_part)
-    assert isinstance(sdk_part.root, TextPart)
-    assert sdk_part.root.text == ''
+    with pytest.raises(ValueError, match='Unsupported part:'):
+        to_sdk_part(stored_part)
 
 
 def test_to_stored_artifact() -> None: