[backend] Fix null field in import

[RomuDeuxfois]

Proposed changes

• Improv property extraction to avoid null values

[codecov]

Codecov Report

Attention: Patch coverage is 7.69231% with 12 lines in your changes missing coverage. Please review.

Project coverage is 32.53%. Comparing base (647b5a2) to head (00d6514).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...main/java/io/openbas/importer/V1_DataImporter.java	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1512   +/-   ##
=========================================
  Coverage     32.53%   32.53%           
  Complexity     1464     1464           
=========================================
  Files           534      534           
  Lines         13777    13775    -2     
  Branches        824      818    -6     
=========================================
  Hits           4482     4482           
+ Misses         9086     9084    -2     
  Partials        209      209           

Flag	Coverage Δ
	32.53% <7.69%> (+<0.01%)	⬆️

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[isselparra]

Functional test OK

Regression detected: there seems to be a regression regarding the creation of an Scenario, when a severity is specified, on the UI it appears as "Unknown". Also the severity attribute (scenario_severity in the json) is "null" after the export of an recently created Scenario. cc @RomuDeuxfois

[RomuDeuxfois]

I fix the regression @isselparra

[isselparra]

Test OK

• The Severity regression is not present anymore
• On import/export the severity was taken into account