T14466 model changedfields

[niden]

Hello!

• Type: Enhancement
• Link to issue: [BUG]: Fatal error on call $model->getChangedFields() #14466

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Small description of change:

Thanks

[codecov]

Codecov Report

Merging #14468 into 4.0.x will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            4.0.x   #14468      +/-   ##
==========================================
+ Coverage   67.66%   67.67%   +<.01%     
==========================================
  Files         482      482              
  Lines      111331   111331              
==========================================
+ Hits        75337    75339       +2     
+ Misses      35994    35992       -2