Fix collect_events returning None instead of empty list for empty expected list (#283)

.changeset/fine-places-pump.md

@@ -0,0 +1,5 @@
+---
+"llama-index-workflows": patch
+---
+
+Return an empty list for empty target events, rather than None

packages/llama-index-workflows/src/workflows/runtime/broker.py

@@ -237,6 +237,10 @@ class WorkflowBroker(Generic[MODEL_T]):
     ) -> list[Event] | None:
         step_ctx = self._get_step_ctx(fn="collect_events")
 
+        # If no events are expected, return an empty list immediately
+        if not expected:
+            return []
+
         buffer_id = buffer_id or "default"
 
         collected_events = step_ctx.state.collected_events.get(buffer_id, [])

packages/llama-index-workflows/tests/context/test_context.py

@@ -57,6 +57,26 @@ async def test_collect_events() -> None:
     assert r.result == [ev1, ev2]
 
 
+@pytest.mark.asyncio
+async def test_collect_events_empty_expected_list() -> None:
+    """
+    Test that collect_events returns an empty list (not None) when the
+    expected list is empty. This edge case should immediately return []
+    since there are no events to collect.
+    """
+
+    class TestWorkflow(Workflow):
+        @step
+        async def start_step(self, ctx: Context, ev: StartEvent) -> StopEvent:
+            # Pass an empty list of expected events
+            events = ctx.collect_events(ev, [])
+            # Should return an empty list, not None
+            return StopEvent(result=events)
+
+    r = await WorkflowTestRunner(TestWorkflow()).run()
+    assert r.result == []
+
+
 @pytest.mark.asyncio
 async def test_collect_events_with_extra_event_type() -> None:
     """

uv.lock

@@ -1644,7 +1644,7 @@ wheels = [
 
 [[package]]
 name = "llama-index-utils-workflow"
-version = "0.7.0"
+version = "0.7.1"
 source = { editable = "packages/llama-index-utils-workflow" }
 dependencies = [
     { name = "llama-index-core" },
@@ -1677,7 +1677,7 @@ dev = [
 
 [[package]]
 name = "llama-index-workflows"
-version = "2.12.0"
+version = "2.12.1"
 source = { editable = "packages/llama-index-workflows" }
 dependencies = [
     { name = "eval-type-backport", marker = "python_full_version < '3.10'" },