fix some mypy lint

postillon/store.py

@@ -15,6 +15,7 @@ class Store:
             self.dbpath = path
         if self.connection is not None:
             return self.connection
+        assert self.dbpath is not None
         self.connection = sqlite3.connect(
             self.dbpath, isolation_level=None
         )  # auto commit
@@ -45,6 +46,7 @@ class Store:
         )
 
     def add(self, posts: Iterable[Post]):
+        assert self.connection is not None
         sql = f"""
             insert into post(content, source, date)
             values (?, ?, ?)
@@ -59,6 +61,7 @@ class Store:
         )
 
     def _select(self, condition="", params=[]) -> Iterable[Post]:
+        assert self.connection is not None
         sql = f"select id, content, date, source from post {condition}"
         for row in self.connection.execute(sql, params):
             id, content, date, source = row
@@ -71,6 +74,7 @@ class Store:
         cond = "where id in (select id from post order by random() limit 1)"
         for post in self._select(cond):
             return post
+        return None
 
     def search(self, term, skip: int = 0) -> Iterable[Post]:
         cond = "where content like ? order by date desc limit -1 offset ?"