[BUG] 완료한캔디: 월별 캔디(카테고리별로 보기)

[LeeJE20]

[GET]~api/candies/monthlyCompletedCandy/:category_id

(node:19684) UnhandledPromiseRejectionWarning: CastError: Cast to date failed for value "Invalid Date" (type Date) at path "reward_completed_at" for model "Candy"
    at model.Query.exec (C:\Project\handycandy\HandyCandy_Server\node_modules\mongoose\lib\query.js:4478:21)
    at model.Query.Query.then (C:\Project\handycandy\HandyCandy_Server\node_modules\mongoose\lib\query.js:4572:15)
    at processTicksAndRejections (internal/process/task_queues.js:95:5)      
(node:19684) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). 
To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 4)