diff --git a/distributed/bridge.py b/distributed/bridge.py
index a180fb47a18..fe83d0aaebc 100644
--- a/distributed/bridge.py
+++ b/distributed/bridge.py
@@ -30,9 +30,11 @@
 from distributed import preloading
 from distributed.core import ConnectionPool
 from distributed.security import Security
-from distributed.utils import LoopRunner, SyncMethodMixin, no_default, sync
+from distributed.utils import LoopRunner, SyncMethodMixin,  sync
 from distributed.utils_comm import gather_from_workers, scatter_to_workers
 
+from dask.typing import no_default
+
 logger = logging.getLogger(__name__)
 
 def _handle_print(event):
diff --git a/distributed/scheduler.py b/distributed/scheduler.py
index 150f73f9bad..1ac2bc4cdca 100644
--- a/distributed/scheduler.py
+++ b/distributed/scheduler.py
@@ -5078,7 +5078,10 @@ def stimulus_external_task_finished(
         ws: WorkerState = self.workers[worker]
         ts: TaskState = self.tasks.get(key)
         if ts.state == "external":
-            ts.metadata.update(kwargs["metadata"])
+            if kwargs["metadata"]:
+                if ts.metadata is None:
+                    ts.metadata = dict()
+                ts.metadata.update(kwargs["metadata"])
             r: tuple = self._transition(
                 key, "memory", stimulus_id, worker=worker, **kwargs
             )