ParseObject.get has side effects for pending operations on nested fields

[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

Pending operations on nested fields of depth at least two get re-done for every call to .get()

Steps to reproduce

1. Create an object with a double-nested integer field:

const obj = new TestObject();
obj.set('objectField', { foo: { bar: 5 } });

2. Save the object to create it:

await obj.save();

3. Increment the nested field:

obj.increment('objectField.foo.bar', 15);

4. Read its value twice:

assert.equal(obj.get('objectField').foo.bar, 20);
assert.equal(obj.get('objectField').foo.bar, 20);

Actual Outcome

The first assert succeeds, the second fails with 35 != 20
Note that without the call to .save(), even the first assert fails with 15 != 20, which might be a separate issue.

Expected Outcome

Both asserts should succeed

Environment

Server

• Parse Server version: 4.5.0
• Operating system: Ubuntu 20.04
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): local

Database

• System (MongoDB or Postgres): MongoDB
• Database version: v4.4.5
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): local

Client

• Parse JS SDK version: master as of 14 May

Logs

[mstniy]

These lines should probably be doing a deep-copy.
Feels like we should also remove line 138 and the spread at line 139.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[mstniy]

Fixed after #1451