Checking that lastViewedElements in ModelQualityFXController.java is

never empty.

Issue-Ref: 4310
Issue-Url: af3#4310


Signed-off-by: Konstantin Blaschke <blaschke@fortiss.org>

org.fortiss.tooling.ext.quality.ui/src/org/fortiss/tooling/ext/quality/ui/view/fx/.ratings

 IModelQualityViewPart.java 708f8089645df12098ea67190805cce343045d2e GREEN
-ModelQualityFXController.java 64c5fb2ca8cca77982b5a20695efcf2b1442045e RED
+ModelQualityFXController.java 68b7df18eff48c9fd5ff87d5641f1f9d47485412 YELLOW
 ModelQualityFXViewPart.java 9cfc7f60a86ea5b915c726b16712f8be7dec2c5f GREEN

org.fortiss.tooling.ext.quality.ui/src/org/fortiss/tooling/ext/quality/ui/view/fx/ModelQualityFXController.java

@@ -328,8 +328,9 @@ public class ModelQualityFXController extends CompositeFXControllerBase<SplitPan
 	private SpiderChartViewer buildSpiderChart() {
 		// Calculate the intersection of the keys, i.e. a set of keys which have a non-null value in
 		// all elements of the lastViewedElements list
-		// TODO (SB): Add check that lastViewedElements is non empty, and add a corresonding comment
-		// to the .get(0) statement
+		
+		// it is never empty due to the fact, that the updateLastViewedEements is always executed before, where the
+		// first element is either null at startup or the before selected one is added to the array.
 		Set<MetricKey> keysIntersection = lastViewedElements.get(0).getValue();
 		for(var p : lastViewedElements) {
 			keysIntersection.retainAll(p.getValue());