All updates to an object field except for the last one are ignored

[mstniy]

New Issue Checklist

• 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 versions of Parse Server and the Parse JS SDK.

Issue Description

When updating multiple nested fields under the same object field using ParseObject.set, all updates except for the last one are dropped.

Steps to reproduce

const obj = new Parse.Object("MyObject");
obj.set("a",{});
await obj.save();
obj.set("a.b", 5);
obj.set("a.c", 6);

Actual Outcome

obj.attributes should be {a: {b:5, c:6}}

Expected Outcome

obj.attributes is {a: {c:6}}

Environment

Server

• Parse Server version: irrelevant
• Operating system: Ubuntu 20.04
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): local, irrelevant

Database

• System (MongoDB or Postgres): MongoDB
• Database version: 5.0.6
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): local

Client

• Parse JS SDK version: alpha (commit d084ac9be058d9b13f8ac2bbf04615f76dc2800d)

Logs

[parse-github-assistant]

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[parseplatformorg]

🎉 This change has been released in version 5.1.0-alpha.7

[parseplatformorg]

🎉 This change has been released in version 5.1.0-beta.1

[parseplatformorg]

🎉 This change has been released in version 5.1.0