fix: preserve empty-string text parts in A2A converter

src/google/adk/a2a/converters/part_converter.py

@@ -179,7 +179,7 @@ def convert_genai_part_to_a2a_part(
 ) -> Optional[a2a_types.Part]:
   """Convert a Google GenAI Part to an A2A Part."""
 
-  if part.text:
+  if part.text is not None:
     a2a_part = a2a_types.TextPart(text=part.text)
     if part.thought is not None:
       a2a_part.metadata = {_get_adk_metadata_key('thought'): part.thought}

tests/unittests/a2a/converters/test_part_converter.py

@@ -297,6 +297,23 @@ def test_convert_text_part_with_thought(self):
     assert result.root.metadata is not None
     assert result.root.metadata[_get_adk_metadata_key("thought")]
 
+  def test_convert_empty_text_part(self):
+    """Test that Part(text='') is preserved, not dropped.
+
+    Regression test for #5341: empty-string text parts are valid and
+    must not fall through to the unsupported-part warning.
+    """
+    # Arrange
+    genai_part = genai_types.Part(text="")
+
+    # Act
+    result = convert_genai_part_to_a2a_part(genai_part)
+
+    # Assert — should produce a valid TextPart, not None
+    assert result is not None
+    assert isinstance(result.root, a2a_types.TextPart)
+    assert result.root.text == ""
+
   def test_convert_file_data_part(self):
     """Test conversion of GenAI file_data Part to A2A Part."""
     # Arrange
@@ -926,9 +943,9 @@ def test_a2a_function_call_with_thought_signature_to_genai(self):
                 _get_adk_metadata_key(
                     A2A_DATA_PART_METADATA_TYPE_KEY
                 ): A2A_DATA_PART_METADATA_TYPE_FUNCTION_CALL,
-                _get_adk_metadata_key("thought_signature"): (
-                    base64.b64encode(b"restored_signature").decode("utf-8")
-                ),
+                _get_adk_metadata_key("thought_signature"): base64.b64encode(
+                    b"restored_signature"
+                ).decode("utf-8"),
             },
         )
     )