add isset tests to fix undefined index PHP notices in RestController

[kouralex]

No description provided.

[codecov]

Codecov Report

Merging #1102 (1a123d8) into master (91a30e5) will increase coverage by 1.72%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #1102      +/-   ##
============================================
+ Coverage     60.32%   62.05%   +1.72%     
- Complexity     1592     1626      +34     
============================================
  Files            32       32              
  Lines          4429     4654     +225     
============================================
+ Hits           2672     2888     +216     
- Misses         1757     1766       +9     

Impacted Files	Coverage Δ	Complexity Δ
controller/RestController.php	11.45% <0.00%> (ø)	193.00 <0.00> (+4.00)
model/sparql/GenericSparql.php	72.59% <0.00%> (+4.54%)	348.00% <0.00%> (+30.00%)

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[osma]

The Travis CI build failure was transient and only happened on PHP 7.2 not other versions, so I will ignore it. Looks good, merging.