Entry returns None ends conversation (#1270)

* Fix unresolvable promises

* added async test and description

* added test_none_on_first_message for conv_handler

* Small change in ConversationHandler docstring

* Fix test to work with new commandhandler

telegram/ext/conversationhandler.py

@@ -64,9 +64,10 @@ class ConversationHandler(Handler):
 
     To change the state of conversation, the callback function of a handler must return the new
     state after responding to the user. If it does not return anything (returning ``None`` by
-    default), the state will not change. To end the conversation, the callback function must
-    return :attr:`END` or ``-1``. To handle the conversation timeout, use handler
-    :attr:`TIMEOUT` or ``-2``.
+    default), the state will not change. If an entry point callback function returns None,
+    the conversation ends immediately after the execution of this callback function.
+    To end the conversation, the callback function must return :attr:`END` or ``-1``. To
+    handle the conversation timeout, use handler :attr:`TIMEOUT` or ``-2``.
 
     Attributes:
         entry_points (List[:class:`telegram.ext.Handler`]): A list of ``Handler`` objects that can
@@ -260,6 +261,8 @@ class ConversationHandler(Handler):
                     self.logger.exception("{}".format(exc))
                     res = old_state
                 finally:
+                    if res is None and old_state is None:
+                        res = self.END
                     self.update_state(res, key)
                     state = self.conversations.get(key)
             else:

tests/test_conversationhandler.py

@@ -84,6 +84,9 @@ class TestConversationHandler(object):
     def start_end(self, bot, update):
         return self._set_state(update, self.END)
 
+    def start_none(self, bot, update):
+        return self._set_state(update, None)
+
     def brew(self, bot, update):
         return self._set_state(update, self.BREWING)
 
@@ -343,6 +346,40 @@ class TestConversationHandler(object):
         # Assert that the Promise has been resolved and the conversation ended.
         assert len(handler.conversations) == 0
 
+    def test_none_on_first_message(self, dp, bot, user1):
+        handler = ConversationHandler(
+            entry_points=[CommandHandler('start', self.start_none)], states={}, fallbacks=[])
+        dp.add_handler(handler)
+
+        # User starts the state machine and a callback function returns None
+        message = Message(0, user1, None, self.group, text='/start', bot=bot)
+        dp.process_update(Update(update_id=0, message=message))
+        assert len(handler.conversations) == 0
+
+    def test_none_on_first_message_async(self, dp, bot, user1):
+        start_none_async = (lambda bot, update: dp.run_async(self.start_none, bot, update))
+
+        handler = ConversationHandler(
+            entry_points=[CommandHandler('start', start_none_async)], states={}, fallbacks=[])
+        dp.add_handler(handler)
+
+        # User starts the state machine with an async function that returns None
+        # Async results are resolved when the users state is queried next time.
+        message = Message(0, user1, None, self.group, text='/start',
+                          entities=[MessageEntity(type=MessageEntity.BOT_COMMAND,
+                                                  offset=0, length=len('/start'))],
+                          bot=bot)
+        dp.update_queue.put(Update(update_id=0, message=message))
+        sleep(.1)
+        # Assert that the Promise has been accepted as the new state
+        assert len(handler.conversations) == 1
+
+        message.text = 'resolve promise pls'
+        dp.update_queue.put(Update(update_id=0, message=message))
+        sleep(.1)
+        # Assert that the Promise has been resolved and the conversation ended.
+        assert len(handler.conversations) == 0
+
     def test_per_chat_message_without_chat(self, bot, user1):
         handler = ConversationHandler(
             entry_points=[CommandHandler('start', self.start_end)], states={},