Fix bug in direct task calls for objects that were evicted (#6216)

* Fix bug and add some checks

* rename

python/ray/serialization.py

@@ -298,7 +298,10 @@ class SerializationContext(object):
             except pyarrow.DeserializationCallbackError:
                 raise DeserializationError()
         else:
-            # Object isn't available in plasma.
+            # Object isn't available in plasma. This should never be returned
+            # to the user. We should only reach this line if this object was
+            # deserialized as part of a list, and another object in the list
+            # throws an exception.
             return plasma.ObjectNotAvailable
 
     def _store_and_register_pyarrow(self, value, depth=100):

python/ray/tests/test_actor.py

@@ -2213,7 +2213,8 @@ def test_actor_eviction(ray_start_object_store_memory):
     num_evicted, num_success = 0, 0
     for obj in objects:
         try:
-            ray.get(obj)
+            val = ray.get(obj)
+            assert isinstance(val, np.ndarray), val
             num_success += 1
         except ray.exceptions.UnreconstructableError:
             num_evicted += 1