fix: Improve error handling in task creation (#294)

# Description

This update improves the robustness of the `new_task` function by adding
explicit error handling for invalid `Message` objects.

Previously, `new_task` did not validate its input, which could lead to
unexpected `TypeError` or `ValueError` exceptions when a malformed
`Message` was passed. This change introduces checks to ensure that a
`Message` has a valid `role` and a non-empty `parts` list before a
`Task` is created.

Additionally, this update includes corresponding unit tests to verify
the new error handling and ensures that the correct exceptions are
raised for invalid inputs.

Author: pankaj-bind

src/a2a/utils/task.py

@@ -15,7 +15,16 @@ def new_task(request: Message) -> Task:
 
     Returns:
         A new `Task` object initialized with 'submitted' status and the input message in history.
+
+    Raises:
+        TypeError: If the message role is None.
+        ValueError: If the message parts are empty.
     """
+    if not request.role:
+        raise TypeError('Message role cannot be None')
+    if not request.parts:
+        raise ValueError('Message parts cannot be empty')
+
     return Task(
         status=TaskStatus(state=TaskState.submitted),
         id=(request.taskId if request.taskId else str(uuid.uuid4())),

tests/utils/test_task.py

@@ -113,6 +113,25 @@ def test_completed_task_uses_provided_history(self):
         )
         self.assertEqual(task.history, history)
 
+    def test_new_task_invalid_message_empty_parts(self):
+        with self.assertRaises(ValueError):
+            new_task(
+                Message(
+                    role=Role.user,
+                    parts=[],
+                    messageId=str(uuid.uuid4()),
+                )
+            )
+
+    def test_new_task_invalid_message_none_role(self):
+        with self.assertRaises(TypeError):
+            msg = Message.model_construct(
+                role=None,
+                parts=[Part(root=TextPart(text='test message'))],
+                messageId=str(uuid.uuid4()),
+            )
+            new_task(msg)
+
 
 if __name__ == '__main__':
     unittest.main()