Variability: Fixed presence condition property section

There was an unnecessary model change for the case in which a element
without a pc was assignes an empty pc. The model is not changed / dirty,
now.

Issue-ref: 4273
Issue-URL: af3#4273

Signed-off-by: Andreas Bayha <bayha@fortiss.org>

org.fortiss.tooling.ext.variability/src/org/fortiss/tooling/ext/variability/util/.ratings

-VariabilityUtils.java 6bab655b72f9b2e53c9dd14b9ea7981cabc5493a YELLOW
+VariabilityUtils.java 3a10f28d57ca4da70b6236b74bd682fa8b03582a YELLOW

org.fortiss.tooling.ext.variability/src/org/fortiss/tooling/ext/variability/util/VariabilityUtils.java

@@ -177,7 +177,14 @@ public class VariabilityUtils {
 		final OptionalVariationPointSpecification finalSpec = spec;
 		// Change model only, if the new presence condition is different from the old one
 		PresenceCondition oldPC = spec.getPresenceCondition();
-		if(oldPC == null || !oldPC.getStringRepresentation().equals(pc.getStringRepresentation())) {
+
+		// If both pc are null, there is nothing to change
+		if(oldPC == null && pc == null) {
+			return true;
+		}
+		// Check whether the old and new are different (i.e. one being null or different value)
+		if(oldPC == null || pc == null ||
+				!oldPC.getStringRepresentation().equals(pc.getStringRepresentation())) {
 			ICommandStackService.getInstance().runAsCommand(elem,
 					() -> finalSpec.setPresenceCondition(pc));
 		}