improve treatment of empty classes

jastadd-mquat-solver-ilp/src/main/java/de/tudresden/inf/st/mquat/solving/ilp/AbstractILPTransformer.java

@@ -39,6 +39,7 @@ public class AbstractILPTransformer implements ILPTransformer {
 
     for (int clusterId : clusters.keySet()) {
 
+      if (clusters.get(clusterId).size() > 0) {
         ResourceClass resourceClass = new ResourceClass();
         resourceClass.setName(new Name("class_" + clusterId));
 
@@ -49,6 +50,8 @@ public class AbstractILPTransformer implements ILPTransformer {
 
         model.getHardwareModel().addResourceClass(resourceClass);
       }
+
+    }
   }