fix: add missing condition when a parent entity is not available

[jacquesfize]

resolves #591

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1315447) to head (dce3044).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop      #592   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines            4         4           
=========================================
  Hits             4         4           

Flag	Coverage Δ
pytest	100.00% <ø> (ø)

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[amandine-sahl]

j'ai bien pu importer les sites, par contre n'ayant pas de groupes de site il ne sont pas visible dans le module uniquement dans le gestionnaire de sites