Don't be such a positive Polly about this bad news.
positive Polly
idiomSomeone who is excessively upbeat, encouraging and optimistic, often to the point where it may seem overly cheerful or naive.
Even when the project failed completely, she acted like a positive Polly and insisted that everything would be fine.
His colleagues grew weary of his constant optimism, often dismissing his suggestions as the naive musings of a positive Polly who refused to acknowledge the gravity of the situation.