[JENKINS-49601] Fix NPE in ReplayCause when replaying Runs. fixes #1401

plugin/src/main/java/org/jenkinsci/plugins/workflow/cps/replay/ReplayCause.java

@@ -64,6 +64,11 @@ public int getOriginalNumber() {
     }
 
     public @CheckForNull Run<?, ?> getOriginal() {
+        // "run" may be null after construction before onAddedTo is called
+        // "run" may be null after deserialization before onLoad is called
+        if (run == null) {
+            return null;
+        }
         return run.getParent().getBuildByNumber(originalNumber);
     }
 

plugin/src/test/java/org/jenkinsci/plugins/workflow/cps/replay/ReplayCauseTest.java

@@ -0,0 +1,71 @@
+package org.jenkinsci.plugins.workflow.cps.replay;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import hudson.model.CauseAction;
+import hudson.model.TaskListener;
+import hudson.util.StreamTaskListener;
+import hudson.util.XStream2;
+import org.jenkinsci.plugins.workflow.cps.CpsFlowDefinition;
+import org.jenkinsci.plugins.workflow.job.WorkflowJob;
+import org.jenkinsci.plugins.workflow.job.WorkflowRun;
+import org.junit.Rule;
+import org.junit.Test;
+import org.jvnet.hudson.test.JenkinsRule;
+
+public class ReplayCauseTest {
+
+    @Rule
+    public JenkinsRule j = new JenkinsRule();
+
+    @Test
+    public void replayCausePrintIsSafeBeforeOnAddedTo() throws Exception {
+        WorkflowJob p = j.createProject(WorkflowJob.class, "p");
+        p.setDefinition(new CpsFlowDefinition("echo 'hello'", false));
+        WorkflowRun original = j.assertBuildStatusSuccess(p.scheduleBuild2(0));
+
+        // construct cause, don't call onAddedTo yet.
+        ReplayCause cause = new ReplayCause(original);
+        assertNull(cause.getRun());
+
+        // verify print() does not throw NPE.
+        TaskListener listener = StreamTaskListener.fromStdout();
+        cause.print(listener);
+
+        // verify getOriginal() returns run after onAddedTo.
+        original.addAction(new CauseAction(cause));
+        assertNotNull(cause.getOriginal());
+    }
+
+    @Test
+    public void replayCausePrintIsSafeAfterDeserializeBeforeOnLoad() throws Exception {
+        WorkflowJob p = j.createProject(WorkflowJob.class, "p2");
+        p.setDefinition(new CpsFlowDefinition("echo 'hello'", false));
+        WorkflowRun original = j.assertBuildStatusSuccess(p.scheduleBuild2(0));
+
+        // Create a new run and attach the cause so run is initially set.
+        WorkflowRun newRun = j.assertBuildStatusSuccess(p.scheduleBuild2(0));
+        ReplayCause cause = new ReplayCause(original);
+        newRun.addAction(new CauseAction(cause));
+        assertNotNull(cause.getRun());
+
+        // serialize and deserialize the cause, which should clear the transient run field.
+        XStream2 xs = new XStream2();
+        String xml = xs.toXML(cause);
+
+        Object obj = xs.fromXML(xml);
+        if (obj instanceof ReplayCause) {
+            ReplayCause deserialized = (ReplayCause) obj;
+            assertNull(deserialized.getRun());
+
+            // getOriginal() is safe to call and returns null until onLoad is called
+            TaskListener listener = StreamTaskListener.fromStdout();
+            deserialized.print(listener);
+
+            // simulate Jenkins calling onLoad to reattach the run (Run.onload() is protected)
+            deserialized.onLoad(newRun);
+            assertNotNull(deserialized.getOriginal());
+        }
+    }
+}