diff --git a/synapse/appservice/__init__.py b/synapse/appservice/__init__.py
index d4a2f02fc259..3862d9c08f38 100644
--- a/synapse/appservice/__init__.py
+++ b/synapse/appservice/__init__.py
@@ -297,7 +297,7 @@ def get_groups_for_user(self, user_id: str) -> Iterable[str]:
             user_id: The ID of the user.
 
         Returns:
-            iterable: an iterable that yields group_id strings.
+            An iterable that yields group_id strings.
         """
         return (
             regex_obj["group_id"]
diff --git a/synapse/appservice/scheduler.py b/synapse/appservice/scheduler.py
index a55bc119cb89..ad3c408519ee 100644
--- a/synapse/appservice/scheduler.py
+++ b/synapse/appservice/scheduler.py
@@ -49,7 +49,7 @@
 components.
 """
 import logging
-from typing import List, Optional
+from typing import List
 
 from synapse.appservice import ApplicationService, ApplicationServiceState
 from synapse.events import EventBase
@@ -120,7 +120,7 @@ def _start_background_request(self, service):
             "as-sender-%s" % (service.id,), self._send_request, service
         )
 
-    def enqueue_event(self, service, event):
+    def enqueue_event(self, service: ApplicationService, event: EventBase):
         self.queued_events.setdefault(service.id, []).append(event)
         self._start_background_request(service)
 
@@ -177,7 +177,7 @@ async def send(
         self,
         service: ApplicationService,
         events: List[EventBase],
-        ephemeral: Optional[JsonDict] = None,
+        ephemeral: List[JsonDict] = [],
     ):
         try:
             txn = await self.store.create_appservice_txn(
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index dbb4887985ca..5cdf16521c3f 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -23,6 +23,7 @@
 from synapse.storage._base import SQLBaseStore, db_to_json, make_in_list_sql_clause
 from synapse.storage.database import DatabasePool
 from synapse.storage.util.id_generators import StreamIdGenerator
+from synapse.types import JsonDict
 from synapse.util import json_encoder
 from synapse.util.async_helpers import ObservableDeferred
 from synapse.util.caches.descriptors import cached, cachedList
@@ -277,7 +278,18 @@ def f(txn):
     @cached(num_args=2,)
     async def get_linearized_receipts_for_all_rooms(
         self, to_key: int, from_key: Optional[int] = None
-    ):
+    ) -> Dict[str, JsonDict]:
+        """Get receipts for all rooms between two stream_ids.
+
+        Args:
+            to_key: Max stream id to fetch receipts upto.
+            from_key: Min stream id to fetch receipts from. None fetches
+                from the start.
+
+        Returns:
+            A dictionary of roomids to a list of receipts.
+        """
+
         def f(txn):
             if from_key:
                 sql = """