CustomNodeManager2 initialize predefined nodes in constructor

[romanett]

Proposed changes

• initialize m_predefinedNodes in constructor
• remove nullabilty checks

Related Issues

• Fixes CustomNodeManager2.AddReverseReferences crashes in foreach loop when m_predefinedNodes is null #2964

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Test enhancement (non-breaking change to increase test coverage)
• Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc.
• I have signed the CLA.
• I ran tests locally with my changes, all passed.
• I fixed all failing tests in the CI pipelines.
• I fixed all introduced issues with CodeQL and LGTM.
• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• I have added necessary documentation (if appropriate).
• Any dependent changes have been merged and published in downstream modules.

Further comments

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.44%. Comparing base (f7815c8) to head (7266d84).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2966      +/-   ##
==========================================
+ Coverage   55.40%   55.44%   +0.04%     
==========================================
  Files         352      352              
  Lines       67859    67853       -6     
  Branches    13908    13904       -4     
==========================================
+ Hits        37598    37623      +25     
+ Misses      26136    26106      -30     
+ Partials     4125     4124       -1     

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