fix: handling metadata catalog null & self rel

[datnguye]

resolves #87

Description

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

Checklist

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

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

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