Fix return type of _return_result

diff --git a/tornado/gen.py b/tornado/gen.py
index 2d203855131561145f15e986a910b0fb7c93a538..a6370259b391c1bb195bb60bd7895cd2d4528ecc 100644 (file)
--- a/tornado/gen.py
+++ b/tornado/gen.py
@@ -410,7 +410,7 @@ class WaitIterator(object):
         else:
             self._finished.append(done)
 
-    def _return_result(self, done: Future) -> None:
+    def _return_result(self, done: Future) -> Future:
         """Called set the returned future's state that of the future
         we yielded, and set the current future for the iterator.
         """