Problem manager bugfix.
diff --git a/org.eclipse.viatra2.core2/src/org/eclipse/viatra2/modelChecker/impl/ProblemManager.java b/org.eclipse.viatra2.core2/src/org/eclipse/viatra2/modelChecker/impl/ProblemManager.java
index 71e77f3..d2be87a 100644
--- a/org.eclipse.viatra2.core2/src/org/eclipse/viatra2/modelChecker/impl/ProblemManager.java
+++ b/org.eclipse.viatra2.core2/src/org/eclipse/viatra2/modelChecker/impl/ProblemManager.java
@@ -52,7 +52,8 @@
 		//	ms.getTransactionManager().beginTransaction();
 			mc = new ModelChecker();
 			
-			if (fw.getProperties().getRuntimeProperty("Model checking", "On-the-fly model checking").equalsIgnoreCase("true"))
+			if (fw.getProperties().getRuntimeProperty("Model checking", "On-the-fly model checking")!=null &&
+					fw.getProperties().getRuntimeProperty("Model checking", "On-the-fly model checking").equalsIgnoreCase("true"))
 			{
 				pc = new ProblemCounter(mc.checkAllModelElement(ms), this);
 				cli = new ConsistencyListener(pc);