diff --git a/subprojects/common/analysis/src/main/java/hu/bme/mit/theta/analysis/algorithm/cegar/CegarChecker.java b/subprojects/common/analysis/src/main/java/hu/bme/mit/theta/analysis/algorithm/cegar/CegarChecker.java
index 677ab071be..60138f604f 100644
--- a/subprojects/common/analysis/src/main/java/hu/bme/mit/theta/analysis/algorithm/cegar/CegarChecker.java
+++ b/subprojects/common/analysis/src/main/java/hu/bme/mit/theta/analysis/algorithm/cegar/CegarChecker.java
@@ -91,10 +91,11 @@ public SafetyResult<S, A> check(final P initPrec) {
             abstractorTime += stopwatch.elapsed(TimeUnit.MILLISECONDS) - abstractorStartTime;
             logger.write(Level.MAINSTEP, "| Checking abstraction done, result: %s%n", abstractorResult);
 
-            String argGraph = JSONWriter.getInstance().writeString(ArgVisualizer.getDefault().visualize(arg));
-            String precString = prec.toString();
-
-            wdl.addIteration(iteration, argGraph, precString);
+            if (wdl != null) {
+                String argGraph = JSONWriter.getInstance().writeString(ArgVisualizer.getDefault().visualize(arg));
+                String precString = prec.toString();
+                wdl.addIteration(iteration, argGraph, precString);
+            }
 
             if (abstractorResult.isUnsafe()) {
                 MonitorCheckpoint.Checkpoints.execute("CegarChecker.unsafeARG");