[JBPM-10188] Signaling process instances (#2319) (#2325)

Original expression needs to be added as it is to external event
listeners. This way it can be converted when persisted.

Co-authored-by: Francisco Javier Tirado Sarti <65240126+fjtirado@users.noreply.github.com>

jbpm-flow/src/main/java/org/jbpm/workflow/instance/impl/WorkflowProcessInstanceImpl.java

@@ -622,10 +622,9 @@ protected void registerExternalEventNodeListeners() {
         for (Node node : getWorkflowProcess().getNodes()) {
             if (node instanceof EventNode && "external".equals(((EventNode) node).getScope())) {
                 String eventType = ((EventNode) node).getType();
+                addEventListener(eventType, EMPTY_EVENT_LISTENER, true);
                 if (isVariableExpression(eventType)) {
                     addEventListener(resolveVariable(eventType), EMPTY_EVENT_LISTENER, true);
-                } else {
-                    addEventListener(eventType, EMPTY_EVENT_LISTENER, true);
                 }
             } else if (node instanceof EventSubProcessNode) {
                 List<String> events = ((EventSubProcessNode) node).getEvents();
@@ -648,10 +647,9 @@ private void unregisterExternalEventNodeListeners() {
         for (Node node : getWorkflowProcess().getNodes()) {
             if (node instanceof EventNode && "external".equals(((EventNode) node).getScope())) {
                 String eventType = ((EventNode) node).getType();
+                removeEventListener(eventType, EMPTY_EVENT_LISTENER, true);
                 if (isVariableExpression(eventType)) {
                     removeEventListener(resolveVariable(eventType), EMPTY_EVENT_LISTENER, true);
-                } else {
-                    removeEventListener(eventType, EMPTY_EVENT_LISTENER, true);
                 }
             }
         }
@@ -909,7 +907,6 @@ private Optional<Object> resolveExpressionVariable(String paramName, VariableRes
             if(factory.isResolveable(paramName)) {
                 return Optional.of(factory.getVariableResolver(paramName).getValue());
             }
-
             return Optional.ofNullable(MVELSafeHelper.getEvaluator().eval(paramName, factory));
         } catch (Throwable t) {
             logger.error("Could not find variable scope for variable {}", paramName);