Handle case where legacy dataset has meta: null

[NevilleS]

Closes #2509

Code Changes

• Update migration upgrade script

Steps to Confirm

n/a

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation:
  • documentation complete, PR opened in fidesdocs
  • documentation issue created in fidesdocs
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md

Description Of Changes

The fix in #2510 isn't quite right - it's also possible for dataset.get("meta", {}) to return None if someone defines a Dataset with a meta key but keeps it null. This can be hard to do locally but happens in practice.

[pattisdr]

thank you @NevilleS

[codecov]

Codecov Report

Base: 88.47% // Head: 88.45% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (f46ef8e) compared to base (b7c69d3).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2524      +/-   ##
==========================================
- Coverage   88.47%   88.45%   -0.02%     
==========================================
  Files         328      328              
  Lines       15959    15959              
  Branches     4433     4433              
==========================================
- Hits        14119    14117       -2     
- Misses       1687     1688       +1     
- Partials      153      154       +1     

Impacted Files	Coverage Δ
src/fides/api/ctl/utils/errors.py	88.23% <0.00%> (-5.89%)	⬇️

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