now getRate returns an empty String by default (helpful in Acceleo)

plugins/org.polarsys.chess.mobius/src/org/polarsys/chess/mobius/utils/TransformationUtil.java

@@ -237,9 +237,15 @@ public class TransformationUtil {
 	}
 	
 	public String getRate(Transition tr){
+		String rate = "";
 		Stereotype stereo = tr.getAppliedStereotype(INTERNALFAULTQN);
-		InternalFault intF = (InternalFault) tr.getStereotypeApplication(stereo);
-		return intF.getOccurrence();
+		if(stereo != null){
+			InternalFault intF = (InternalFault) tr.getStereotypeApplication(stereo);
+			if (intF.getOccurrence() != null){
+				rate = intF.getOccurrence();
+			}
+		}
+		return rate;
 	}
 	
 	public List<Classifier> getSubsystems(Classifier parent){