Just a minor thing, for potential refactoring: TopLayerSingletonFramesSelector: public Iterable<? extends WindupVertexFrame> getFrames(GraphRewrite event, EvaluationContext context) { Variables variables = Variables.instance(event); this.varName = Iteration.getPayloadVariableName(event, context); return variables.findVariable(varName); } public static String getPayloadVariableName(GraphRewrite event, EvaluationContext ctx) throws IllegalStateException { Variables variables = Variables.instance(event); Map<String, Iterable<? extends WindupVertexFrame>> topLayer = variables.peek(); if (topLayer.keySet().size() != 1) throw new IllegalStateException("Cannot determine Iteration payload variable name because the top " + "layer of " + Variables.class.getSimpleName() + " stack contains no or multiple variables: " + topLayer.keySet()); String name = topLayer.keySet().iterator().next(); return name; } So it verifies that the Variables stack has only one name, then returns it to let the calling code return the content of that single variable. I think the logic should be reversed - the check for a single variable should be in the calling code. Ondra _______________________________________________ windup-dev mailing list windup-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/windup-dev