made returns from next task consistent to avoid typeerrors, also linear now checks for none

fixes #11965

lib/ansible/executor/play_iterator.py

@@ -130,7 +130,7 @@ class PlayIterator:
 
         task = None
         if s.run_state == self.ITERATING_COMPLETE:
-            return None
+            return (None, None)
         elif s.run_state == self.ITERATING_SETUP:
             s.run_state = self.ITERATING_TASKS
             s.pending_setup = True

lib/ansible/plugins/strategies/linear.py

@@ -58,6 +58,9 @@ class StrategyModule(StrategyBase):
                 continue
 
             (s, t) = v
+            if t is None:
+                continue
+
             if s.cur_block < lowest_cur_block and s.run_state != PlayIterator.ITERATING_COMPLETE:
                 lowest_cur_block = s.cur_block