fix some mypy lint

feeder/store.py

@@ -17,7 +17,7 @@ class Store:
         if path:
             self.dbpath = path
         if self.connection is not None:
-            return self.connection
+            return
         log.debug("Connecting to %s", self.dbpath)
         self.connection = sqlite3.connect(
             self.dbpath, isolation_level=None
@@ -30,6 +30,7 @@ class Store:
             conn.close()
 
     def init(self) -> None:
+        assert self.connection is not None
         conn = self.connection
         conn.execute(
             """
@@ -57,6 +58,7 @@ class Store:
 
     def sync_feeds(self, feeds: Dict[str, Feed]) -> None:
         """Write the current state of feeds to store, and load existing info back."""
+        assert self.connection is not None
         conn = self.connection
         conn.executemany(
             """
@@ -117,6 +119,7 @@ class Store:
             select id, content, date, link, title from post
             where feed_id=? and id in ({qs})
         """
+        assert self.connection is not None
         conn = self.connection
         posts = [Post(*row) for row in conn.execute(sql, (feed_id, *post_ids))]
         for post in posts: