Fix null-handling of skosmos:sparqlGraph

[danmichaelo]

The skosmos:sparqlGraph vocabulary property is listed as optional, but when not set, Skosmos will produce a notice:

Notice:  Trying to access array offset on value of type null in /var/www/html/model/sparql/GenericSparql.php on line 155

The first commit:

• Adds a null check to the GenericSparql::isDefaultEndpoint() method.
• Moves the null check from GenericSparql::generateFromClause() to GenericSparql::getVocabGraphs() and updates the former method to use the latter to reduce code duplication.
• Updates docstrings to use string|null

The second commit:

• Updates GenericSparql::formatFilterGraph to not add a FILTER clause if none of the vocabularies have a skosmos:sparqlGraph. This adreses the issues where you would always get zero results if you didn't specify skosmos:sparqlGraph for any vocabulary, since that would result in this: FILTER (?graph IN ()).

Note: Apart from the case skosmos:sparqlGraph is not defined for any vocabulary, there is also the case where skosmos:sparqlGraph is specified for some of the vocabularies, but not for others. In that case, the default search will only return results for the vocabularies that do specify skosmos:sparqlGraph, which is potentially confusing I guess. Perhaps it should be noted in the docs that it's a good idea to either include skosmos:sparqlGraph for all vocabularies or for none?

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
1 Code Smell

No Coverage information
0.0% Duplication

[osma]

Thanks, I will review it soon!

[codecov]

Codecov Report

Merging #930 into master will increase coverage by 7.44%.
The diff coverage is 75%.

@@             Coverage Diff              @@
##             master     #930      +/-   ##
============================================
+ Coverage     57.62%   65.06%   +7.44%     
  Complexity     1489     1489              
============================================
  Files            32       32              
  Lines          4170     3690     -480     
============================================
- Hits           2403     2401       -2     
+ Misses         1767     1289     -478

Impacted Files	Coverage Δ	Complexity Δ
model/Model.php	83.68% <ø> (+3.36%)	105 <0> (ø)	⬇️
model/Vocabulary.php	88.23% <ø> (+1.09%)	107 <0> (ø)	⬇️
model/sparql/GenericSparql.php	92.75% <75%> (+24.67%)	303 <0> (+1)	⬆️
model/resolver/LOCResource.php	0% <0%> (ø)	6% <0%> (ø)	⬇️
model/resolver/WDQSResource.php	0% <0%> (ø)	3% <0%> (ø)	⬇️
controller/Controller.php	13.79% <0%> (+0.3%)	38% <0%> (ø)	⬇️
controller/RestController.php	4.55% <0%> (+0.56%)	147% <0%> (ø)	⬇️
model/Request.php	67.07% <0%> (+0.8%)	50% <0%> (ø)	⬇️
model/ConceptPropertyValue.php	80.24% <0%> (+0.97%)	46% <0%> (ø)	⬇️
model/PluginRegister.php	70.14% <0%> (+1.03%)	28% <0%> (ø)	⬇️
... and 15 more

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[osma]

Hmm the Codecov report looks surprising. I'm pretty sure this PR won't increase coverage by over 7 % :)

[osma]

Thanks, looks good and I merged it.

I fixed a couple of minor issues (based on Scrutinizer complaints) in subsequent commits.