diff --git a/pipeline-model-definition/src/main/java/org/jenkinsci/plugins/pipeline/modeldefinition/actions/ExecutionModelAction.java b/pipeline-model-definition/src/main/java/org/jenkinsci/plugins/pipeline/modeldefinition/actions/ExecutionModelAction.java
index 531b09352..acba4ef72 100644
--- a/pipeline-model-definition/src/main/java/org/jenkinsci/plugins/pipeline/modeldefinition/actions/ExecutionModelAction.java
+++ b/pipeline-model-definition/src/main/java/org/jenkinsci/plugins/pipeline/modeldefinition/actions/ExecutionModelAction.java
@@ -35,7 +35,7 @@
 public class ExecutionModelAction extends InvisibleAction {
     private ModelASTStages stages;
     private String stagesUUID;
-    private final List<ModelASTStages> stagesList = new ArrayList<>();
+    private List<ModelASTStages> stagesList = new ArrayList<>();
 
     public ExecutionModelAction(ModelASTStages s) {
         this.stagesList.add(s);
@@ -49,7 +49,11 @@ public ExecutionModelAction(List<ModelASTStages> s) {
 
     protected Object readResolve() throws IOException {
         if (this.stages != null) {
+            if (this.stagesList == null) {
+                this.stagesList = new ArrayList<>();
+            }
             this.stagesList.add(stages);
+            
             this.stages = null;
         }
         return this;