Apply suggestions from code review

Co-authored-by: Richard van der Hoff <[email protected]>

synapse/handlers/federation_event.py

@@ -1623,7 +1623,7 @@ async def _check_for_soft_fail(
                     event.room_id,
                     room_version,
                     state_sets,
-                    event_map={},
+                    event_map=None,
                     state_res_store=StateResolutionStore(self._store),
                 )
             )

synapse/handlers/message.py

@@ -1028,11 +1028,11 @@ async def create_new_client_event(
             for state_id in state_event_ids:
                 data = metadata.get(state_id)
                 if data is None:
-                    raise Exception("State event not persisted %s", state_id)
+                    raise Exception(f"State event {state_id} not persisted")
 
                 if data.state_key is None:
                     raise Exception(
-                        "Trying to set non-state event as state: %s", state_id
+                        f"Trying to set non-state event {state_id} as state"
                     )
 
                 state_map[(data.event_type, data.state_key)] = state_id

synapse/state/__init__.py

@@ -273,10 +273,10 @@ async def compute_event_context(
 
         Args:
             event:
-            state_ids_before_event: The event ids of the state at the event if
+            state_ids_before_event: The event ids of the state before the event if
                 it can't be calculated from existing events. This is normally
                 only specified when receiving an event from federation where we
-                don't have the prev events for, e.g. when backfilling.
+                don't have the prev events, e.g. when backfilling.
             partial_state: True if `state_ids_before_event` is partial and omits
                 non-critical membership events
         Returns: