fix: ParseUser.save fails when user is logged in

[mbfakourii]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Issue Description

fix save user

Closes: #819

Approach

Use the new method to send Json in fromJson

TODOs before merging

• Add tests
• Add changes to documentation (guides, repository pages, in-code descriptions)
• A changelog entry

[parse-github-assistant]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[parse-github-assistant]

I will reformat the title to use the proper commit message syntax.

[codecov]

Codecov Report

Base: 15.86% // Head: 15.88% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (1bf66d6) compared to base (664689c).
Patch coverage: 40.00% of modified lines in pull request are covered.

❗ Current head 1bf66d6 differs from pull request most recent head d3b7d2e. Consider uploading reports for the commit d3b7d2e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #822      +/-   ##
==========================================
+ Coverage   15.86%   15.88%   +0.01%     
==========================================
  Files          47       47              
  Lines        2861     2865       +4     
==========================================
+ Hits          454      455       +1     
- Misses       2407     2410       +3     

Impacted Files	Coverage Δ
packages/dart/lib/src/objects/parse_base.dart	46.49% <40.00%> (-0.79%)	⬇️

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[mtrezza]

Is this bug only affecting ParseUser.save, or does it also affect other objects? Could you give more details about the issue, so we can write a proper PR title / changelog entry?

[mbfakourii]

Is this bug only affecting ParseUser.save, or does it also affect other objects? Could you give more details about the issue, so we can write a proper PR title / changelog entry?

This error is related to fromJson when server json values want to be converted to local model

[mtrezza]

Looks good!