Invalid date iso with beforeSave make server unhandled promise rejection and request hanging

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server.

Issue Description

Have a class with a column type Date. Try post with empty string as iso. Get proper error back

{
    "code": 111,
    "error": "This is not a valid Date"
}

Add beforeSave to the class and post again. Request will hang there forever. Server will fail with the following errors

(node:63110) UnhandledPromiseRejectionWarning: Error: Tried to encode an invalid date.
    at encode (/Users/gordon/workspace/pipe17/pipe17-group/parse/node_modules/parse/lib/node/encode.js:85:13)
    at _default (/Users/gordon/workspace/pipe17/pipe17-group/parse/node_modules/parse/lib/node/encode.js:132:10)
    at SetOp.toJSON (/Users/gordon/workspace/pipe17/pipe17-group/parse/node_modules/parse/lib/node/ParseOp.js:155:32)
    at ParseObject._getSaveJSON (/Users/gordon/workspace/pipe17/pipe17-group/parse/node_modules/parse/lib/node/ParseObject.js:485:61)
    at success (/Users/gordon/workspace/pipe17/pipe17-group/parse/node_modules/parse-server/lib/triggers.js:385:45)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
(Use `node --trace-warnings ...` to show where the warning was created)

• 🤩 I will submit a PR with a fix (but probably need someone else do a proper fix)

Environment

Server

• Parse Server version: 4.5.0

Start with the beforeSave trigger flow in parse-server/lib/triggers.js and the error path shown in the Parse encode stack trace. Reproduce a Date field submitted with an empty ISO string, both with and without beforeSave; done means the request returns a proper error without hanging or producing an unhandled promise rejection.