fix: handling metadata catalog null & self rel

[datnguye]

resolves #87

Description

• Handling metadata catalog null
• Supporting Self-relationship with 1 parent model

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f704cf8) 100.00% compared to head (dc0e204) 100.00%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #90   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files           32        32           
  Lines          959       965    +6     
=========================================
+ Hits           959       965    +6     

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