Partial fix for mypy issues

webserver/handlers/api/solar_conditions.py

@@ -28,6 +28,7 @@ class APISolarConditionsHandler(tornado.web.RequestHandler):
 
     def get(self) -> None:
         try:
+            assert self._solar_conditions is not None, "initialize() must be called before get()"
             self.write(self._solar_conditions.to_json())
             self.set_status(200)
             self.set_header("Cache-Control", "no-store")