update

state_machine_exporter/src/main/java/click/kamil/springstatemachineexporter/analysis/service/AbstractCallGraphEngine.java

@@ -629,6 +629,9 @@ public abstract class AbstractCallGraphEngine implements CallGraphEngine {
     }
 
     protected String resolveArgument(Expression expr) {
+        if (expr == null) {
+            return "null";
+        }
         if (expr instanceof LambdaExpression le) {
             ASTNode body = le.getBody();
             if (body instanceof Expression bodyExpr) {

state_machine_exporter/src/main/java/click/kamil/springstatemachineexporter/analysis/service/JdtCallGraphEngine.java

@@ -124,6 +124,9 @@ public class JdtCallGraphEngine extends AbstractCallGraphEngine {
 
     @Override
     protected String resolveArgument(org.eclipse.jdt.core.dom.Expression expr) {
+        if (expr == null) {
+            return "null";
+        }
         // Extract from constructor args (e.g., new CustomMessage(OrderEvent.PROCESS, ...))
         org.eclipse.jdt.core.dom.Expression unwrappedBuilder = unwrapMessageBuilder(expr);
         if (unwrappedBuilder != expr) {