Product Line Analysis: Enables access to null elements of translation

The map if EClass to Z3 null elements can be accessed via a getter.

Issue-ref: 4240
Issue-URL: af3#4240

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

org.fortiss.variability/src/org/fortiss/variability/analysis/ProductLineBaseAnalysis.java

@@ -249,7 +249,8 @@ public class ProductLineBaseAnalysis {
 
 			FuncDecl selFun = translation.eClass2SelectionFunction.get(cls);
 			BoolExpr selected = (BoolExpr)ctx.mkApp(selFun, var);
-			BoolExpr notNull = ctx.mkNot(ctx.mkEq(var, translation.eClass2NullElement.get(cls)));
+			BoolExpr notNull =
+					ctx.mkNot(ctx.mkEq(var, translation.getEClass2NullElement().get(cls)));
 
 			selExprs[i] = ctx.mkAnd(selected, notNull);
 		}

org.fortiss.variability/src/org/fortiss/variability/analysis/ProductLineBaseTranslation.java

@@ -793,4 +793,9 @@ public class ProductLineBaseTranslation {
 	public Context getContext() {
 		return ctx;
 	}
+
+	/** Returns eClass2NullElement. */
+	public Map<EClass, Expr> getEClass2NullElement() {
+		return eClass2NullElement;
+	}
 }